I have to disagree with William Lau.

I think that blog commenting has changed a bit.  It think it is still relevant.  I prefer the term Comment Marketing and Link Earning because that is my goal, to market my site and earn links.  Here is how I do it now.

I find blogs that are relevant to my industry and of people who I really want to have link to me (authority figures).  I follow their blogs and comment regularly on them.  My goal is to build up enough trust and awareness of what I am all about.  I have two goals here.  1) if my comments are good then people will want to learn more about me and click on my profile/link to go to my site (not so much for SEO purposes but for site traffice) ( I don't care if I'm number one if no one goes to my site.  Traffic is important to me.  Even better, relevant traffic.) and 2) I want to be able to eventually earn the right to become a guest blogger or have that person read about me and link to my site because of it's good content.

I think the idea of posting a comment for the sake of posting a comment is pointless.  SEO is changing (for the better) and SEO now should stand for Search EXPERIENCE Optimization and not Search Engine Optimization.  Comment Marketing is relevant if you use it to help build traffic and not to earn "traditional SEO links".

You should be able to head over to https://moz.com/subscriptions (while signed in) and see the option there.

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Firstly, 404s are a natural part of the web and don't think it will kill your site.  It won't.  When you get a 404 error iit can mean that something is pointing to that page or that Google has seen the page before but now it's not there.  Google wants to make sure that that page is completely gone and not an accident to the 404.  Technically if you have nothing pointing to the old post (no external links coming in and no internal links either, including sitemaps) then it will go away after a few crawls.  If you do however have off-page links coming into that page a 301 would definitely be a good idea (best idea would be to get those sources to change the link to the new page url but that's not always possible.  Remember, when you 301 you do loose some link juice)

If you are on Wordpress there are some great plugins to do this like the 301 redirect option on Wordpress SEO by Yoast

If you need to do this manually then let us know and we'll give you the actual code to do it in your .htaccess

Don't let your budget determine your strategy.  I'm not a fan of spending money because you have it.  I would focus on making sure that the clicks you are getting are actually turning into paying customers for the business and once you can confirm that the clicks are actually working for you, then you can scale up your campaign. But it can be done.  I have a client campaign running that I spend $15,000 per month on and still maintain a >4.5% CTR.  So don't let your budget decide your strategy, let what's working decide and scale it upward.

Giving specific advice on your campaign is tough because we don't know if it's a local campaign, product campaign, affiliate campaign, etc.

You asked, "And should each campaign have its own set of unique keywords? Should these keywords never appear in more than 1 campaign?"

Quick answer:  1. Campaigns should have adgroups that target their own niche and then those adgroups should have their own ads that target specific set of keywords.  2. I personally feel that if you do #1 right then keywords will not appear in multiple adgroups.

I like to build adgroups around 1 product and then ads based on keywords that are intuitive for that search and then I target each of those keywords with their own CPC.  For instance, if I'm selling widgets I'll set up a campaign called widgets, an adgroup called blue widgets, and then have keywords like blue widgets, buy blue-green widgets, light blue widgets.  I'll then try to target each of those keywords with their own CPC instead of setting the at the adgroup level.  I also try to make sure that all my keywords in my ad groups are "phrase match" instead of broad or exact.  And, like Sam mentioned, I negative keyword out keywords that don't relate to my strategy.  For instance if you only sell new items, you could add the negative keywords -refurbished, -old, etc.

I don't use PPC like most pros however,  I try to only target people who need "Now" things and keep the competitive shoppers to the organic side.  This will generally help keep your cost down and conversions up.  There are some tricks and things you can do in the title and text to help get only now shoppers.  Also, enhanced campaigns in AdWords now get higher Quality Scores so I would definitely look into optimizing that along with each landing page you have on your own site.

Here is some information on enhanced campaigns from Google.

I'll repeat myself again, but let your goals decide what your strategy is and not your "lack of budget spending".  I generally tell clients that I need $10,000 per month on a campaign but only spend roughly $7,000 or so.   As your quality score and CTR increases, your CPC will go down.   If you worked for me and weren't spending all of the budget I gave you and we were still meeting our goals, you'd be getting a bonus.

Hope that helps.

Moz is great because it provides metrics and information about your site.  SEO is still an art and a science.  The tools that Moz has won't rank your site.  They will help provide invaluable information about your site.  You'll still have to choose the best path for your marketing strategy.  For example, if Moz tells you that you have 25 pages of duplicate content, it doesn't do anything for you unless you know how to act on that information.  If you haven't done so already, I highly recommend reading over Moz's beginner guide to SEO. I'm not saying you should learn SEO (you probably already know alot) but the guide has information in it that may help you think about how to use the tools that Moz offers.  (http://moz.com/beginners-guide-to-seo)

I run a few campaigns in Moz and each of them are set up completely different. Here is a help guide for each of the tools here on Moz and how they can be used to extract data.  http://moz.com/help/guides/research-tools.  If you look at the left sidebar, you'll see links to the specific tools.  On each of those tabs there are videos, a how-to section and FAQs.  By going through each tool and seeing what each does, you'll be able to see how to effectively use the tools to generate the type of data you need to develop an awesome web strategy.

Simple answer is Both.

Having variations of your keyword on a given page will help with rankings for both keywords.  I assume (we all know what happens when we do this) Google will consider these synonyms and after I did the following search strings www.google.com/search?q=e-commerce&pws=0 and then google.com/search?q=ecommerce&pws=0 I think my assumptions are correct.  There is a mix of e-commerce and ecommerce in the both SERPs.  That being said, I would have both variations on my page.  It should natuarally be linked to both ways and with co-citations working in SERPs, it won't really matter.  If you just "built" links to your page with one version, that won't be very natural.  I personally would add e-commerce a few times and ecommerce a few times (if appropriate).

On a personal level, I think of e-commerce not ecommerce.

Google on Synonyms: http://googleblog.blogspot.com/2010/01/helping-computers-understand-language.html

Matt Cutts on Variations of Words: https://www.youtube.com/watch?v=NpnnXt7CHMU

The answer to your question is NO but it is in the pipeline.

In the mean time, what you can do is actually build reports and add recipients to it.  You can have these reports emailed automatically to someone however.  That is what I do for my clients and my team.  That way everyone has the same data at the same time.

Campaigns>Settings(for the particular campaign)>Reports>Add New Report>

If you expand the section under "Build Report" you can click on the reports you want each person to have.  If you want to make sure that each section of the report is exactly what you are looking for, there is actually a little blue link that shows example of what that report will look like.

The only issue is that these are generally summaries and not deep dives in to things like duplicate pages.  I get around this by each week when I get the email from Moz, I go into the campaign and EXPORT all of the deep stuff into a CVS and share it in a Google Doc folder that everyone involved uses.

I think having the ability for someone to be added to a particular campaign would be a great idea though.  Especially when you have multiple people working on a project.  Here is a link that was started some time ago asking Moz for the ability to add additional users to a campaign.  Karen from Moz talks about it in there too so check it out.