Get iOS or Google Play link of app and paste it on SDTT (Structured Data Testing Tool).

That's all. In SDTT they're even deep than 3 points...

Mobile dev here!

So for all stores (AppStore + GooglePlay + Microsoft Marketplace + Amazon App Store + etc) algorithm is simple - they calculate ALL ratings on all versions. Some of them only for local store, other for global.

Example Duolungo:
https://itunes.apple.com/bg/app/duolingo-learn-spanish-french/id570060128?mt=8 <- this is in local Bulgarian Market. 4.928 in 9 ratings.
https://itunes.apple.com/us/app/duolingo-learn-spanish-french/id570060128?mt=8 <- in US market. 4.791 in 4068 ratings.
https://play.google.com/store/apps/details?id=com.duolingo&hl=en <- Worldwide. 4.648 in 2343538 ratings.

As you can see sites provide correct review rating to Google but they rounding it. Probably your guess for over 4.75 is correct. There isn't official explanation from Google about this. Some sites showing 5 star rating system. Other 10 star - 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5. For other it's complicated because i have seen even results as 4.2 and this is 100 star rating system.

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".

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.

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.

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".

Well including sitemap in robots.txt is good praticle but isn't required. You can add sitemap in SearchConsole (or Bing WMT) and bots will index site again. Even bots can index site w/o sitemap but sitemap helps them.

That's why don't worry. You can edit your robots.txt at anytime and add sitemap if it's possible.

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.

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.

Merging all domains under one will be best for you and your client. Here is proof:
https://moz.com/blog/2-become-1-merging-two-domains-made-us-an-seo-killing

But isn't just consolidation, you need to make silo structure, content changes, redirects and many other internal changes.

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.