TL;DR - Yes, you should use both for better CTR in SERP and Social Networks.

OpenGraph is described here:
http://ogp.me/
and OG is mostly used from Facebook and G+.

Twitter used TwitterCards:
https://dev.twitter.com/cards/getting-started#opengraph only for them.

G+ used shema.org or OG:
https://developers.google.com/+/web/snippet/ 
https://developers.google.com/+/web/snippet/article-rendering

Pinterest used RichPins:
https://developers.pinterest.com/docs/rich-pins/overview/

So you should read excellent article from Cyrus Shepard about all meta tags:
https://moz.com/blog/meta-data-templates-123
where everything is described with examples.

And answer is YES! Today is 2015 and within few days will be 2016. Today shares in social networks are so much important than also baclkinging. Of course organic visits and visits from social networks are different, so you need to implement both of tags to get maximum performance there.

If you wish to see performance of KWs or pags you can see few tricks from today post in Moz:
https://moz.com/blog/single-best-seo-tip-for-improved-web-traffic
Yes - SearchConsole is heavy involved in process.

Well there are 4 types of multi-lingual or multi-regional sites that are described here:
https://support.google.com/webmasters/answer/182192?hl=en
Summary - best is ccTLD, next is subdomain with gTLDS. On 3rd is subdirectory with gTLDS and URL parameters is last.

So Moz is trying to diving expert advise to webmasters to NOT use subdomains and giving famous blog example. I fall in this trap almost 15 years ago with subdomain. I wish someone to told me about this then... Other examples can be catalog and different products (catalog.example.com vs. example.com/catalog; product.example.com vs. example.com/product/). This advice in same subdomain keep link juice inside, but you probably know this.

GSC allow setting different directories to specific geo-location. That's true. But you can't change server location with subdirectories. With subdomain this is possible. Example - one company with site of Spanish and German. With subdirectory i have one server and /de and /es folders. But in this case server location is one and only. And server IP is some of signals for geo-targeting so you have tough choice where to be. With subdomain you can make de.example.com and place this in German server and es.example.com and place this in Spanish server.

That's why subdomains for multilingual sites is notable exception of golden rule "do not use subdomains".

And this is the point where you clearly can see that RWD (responsive web design) isn't "one-size-fit-all" solution.

You have few choices but all are weird - double menu, hamburger + kebap menu, sticky menu on left, etc. But as i said this is weird. And only A/B test can show how they works.

I think that best in your case is to try sticky menu on top. One of best example is here:
http://getskeleton.com/
but you need to watch this on desktop. When you scroll down you can see that "Intro Code Examples More" is sticky on top. In your site you need to make changes to "Gallery Partners Pricing". This menu can be sticky even for desktop. This will bring more size in width for main content.

As i said - only A/B test can show who's right. Because all double menus have better navigation but in reality confuses user with "paradox of choice".

Just as Dmitrii says this is UTM is for tracking special campaigns.

But you can't track organic visits because bot crawl your website and find pages A, B, C, etc. And later in SERP you can see A, B ,C and rest pages as-is their physical location. Example http://www.example.com/a.html but you can't see tagged URL in SERP.

This make things impossible for implementing in their request.

If they really, really, really want to be URL tagged - you need to change their canonical of pages and internal linking between pages where all links to be tagged too. And this is pure recipe for SEO disaster. Also will be disaster for Analytics tracking because all traffic will be tagged.

Skeleton have JS to NOT include sticky menu on mobile. But was nice example about mine idea and first that i remember quick during writing this comment.

Second idea is sticky menu with "Hamburger_icon Gallery Partners Price" for mobile and normal (just as now) for desktop. This probably can skip confusing users about menu and hierarchical structure of your website.

But as i said - A/B testing is needed.

You can also have multiple sitemaps on 3rd sites. Look at Moz robots.txt:
Sitemap: https://moz.com/blog-sitemap.xml
Sitemap: https://moz.com/ugc-sitemap.xml
Sitemap: https://moz.com/profiles-sitemap.xml
Sitemap: http://d2eeipcrcdle6.cloudfront.net/past-videos.xml
Sitemap: http://app.wistia.com/sitemaps/36357.xml

Also Google.com robots.txt:
Sitemap: http://www.gstatic.com/culturalinstitute/sitemaps/www_google_com_culturalinstitute/sitemap-index.xml
Sitemap: http://www.gstatic.com/dictionary/static/sitemaps/sitemap_index.xml
Sitemap: http://www.gstatic.com/earth/gallery/sitemaps/sitemap.xml
Sitemap: http://www.gstatic.com/s2/sitemaps/profiles-sitemap.xml
Sitemap: http://www.gstatic.com/trends/websites/sitemaps/sitemapindex.xml
Sitemap: https://www.google.com/sitemap.xml

Also Bing.com robots.txt:
Sitemap: http://cn.bing.com/dict/sitemap-index.xml
Sitemap: http://www.bing.com/offers/sitemap.xml

So using multiple sitemaps it's OK and they can be also hosted on 3rd party server.

Well everything is doable - but remember about users first.

So - lets imagine that i'm looking for someone to be official photograph of mine wedding or engagement or baby photo session. So first if i look is text "i'm photograph that can make your special events memorable...". Ok - you have such text. Second is gallery, 3rd some reviews and pricing. Now in mobile design people just can't reach to them and you get visits with 1 page per session. Right?

That's why i think that "Hamburger Gallery Partners Price" could work. Hamburger is actual menu as now - just need to make it sticky with "Gallery Partners Price". WHY?

Let's assume that i'm on mobile and browsing for "Edinburgh wedding photographer". I see results (term is SERP - search engine result pages) and i click on your site. So i start reading your texts. And as i scroll down to them - sticky menu appear on top. And users can click on them - in result you can have user convinced that "here is the man". So they can give you a call or fill contact form.

2nd Idea - place somewhere in sticky menu "phone" icon that will be linked to your phone using "callto:here-is-your-phone-number". So give user another way to book you.

Well if both sitemaps are for same site then it's OK. But it's much better to implement hreflang as this is explained here:https://support.google.com/webmasters/answer/2620865?hl=en

I'm not sure that Magento can do this but you always can hire 3rd party dev for building plugin/module for this.

I just browse via Google.IT for "vangogh" and you're on N:2 spot after Italian Wikipedia article. I strongly recommend you to create account in SearchConsole and verify your site. There you can see in SearchTraffic exactly what position you get in SERP results.

Now answer for browsers - modern search engines return SERP pages optimized for specific browsers. That's why it's possible browser X to see some results, browser Y to get other results. There is no way to escape this unless you change "user-agent" string in browser with some plugin. Some engines are even going further that return personalized results based on IP, previous searches from this IP, previous searches from this account, previous clicks on SERP, etc.

The only way to get right position is with SearchConsole or special tracking tools as Moz RankTracker. And there you can see "average position".

Yup. Phone will be real and have confirmation to avoid incidental clicks.
No - adding subcats into menu will make navigation heavy for mobile users. Click hamburger, click category, click subcategory, click sub-subcategory. No way someone to nagivate there.

I sent you mine contacts on your site where we can discuss "boring details".

Tuff situation. Why? Browser didn't sent # and everything behind it to the server.

So if you trying to get url as http://www.example.com/#!my-super-duper-url
Browser will sent to the server request for http://www.example.com/ and server will process it. But full url that browser want is also included #! fragment. This mean that you can't make .htaccess redirect, nor some server side redirects for the moment.

So same hurt also all bot and crawlers (Including Moz Roger!). And there was solution:
https://developers.google.com/webmasters/ajax-crawling/docs/specification?hl=en
but later this solution was deprecated:
https://googlewebmastercentral.blogspot.bg/2015/10/deprecating-our-ajax-crawling-scheme.html

And this make things complicated. For now they still support old solution so will be OK for bots. Probably for some users that comes from bookmarks, emails and/or other traffic sources can have hard times. Because will be redirected to "homepage". So maybe combination of both methods (JS redirector + your actual method) can save the day for humans and bots.

True - potential impact can't be seen. But we have few awesome articles about this:
http://www.stateofdigital.com/optimising-urls-seo-ux/
https://moz.com/blog/site-architecture-for-seo
https://moz.com/blog/ugly-seo-mess-recovery-case-study <- checkout "flat structure"

So you now don't have silo structure in your site and he didn't works works. There are many authors about silo structure - Yoast, Bruce Clay, Glenn Gabe, etc. I can suggest to educate little bit about that and implement some structure. Of course redirect 301 old pages to new ones.

Yes - but there is one thing that you should know. Once you enable RegEx ALL your parameters in funnel should be regexed.

https://support.google.com/analytics/answer/1116091?hl=en#matchTypes

"Match Types: Begins with, Equals to, & Regular Expression
There are three diferent match types that define how Analytics identifies a URL for either a goal or a funnel. The match type that you select for your goal URL also applies to the URLs in the funnel, if you create one."

Here is example of Rich Snippet w/o offer (with price):

ACME
  Executive Anvil
 
  Sleeker than ACME's Classic Anvil, the
    Executive Anvil is perfect for the business traveler
    looking for something to drop from a height.

Product #: 925872
  4.4 stars, based on 89 reviews

As you can see this code can be validated and works OK. Now you need to go back in Woo and make "patch" to remove http://schema.org/Offer where is price located. OR temporary disable them.

Hello there!

In GA you tracks site by "code ID". So any site that have code will be tracked.

Few months ago i migrate site from XYZ.machine to XYZmachine.com without changing GA code. And GA still collecting data for sites without changing code at all.

Peter

I don't know what kind of Woo + WordPress + theme you use. But you can download everything into separate folder and use tool to find text in all files. You just need to look who is responsible for "schema.org/Offer" adding into HTML.

Here is shoot in the dark:
https://webdesires.co.uk/blog/add-schema-to-woocommerce-products/
you just need to reverse this change.

As i said - it's just guessing. Can be also in plugin somewhere.