Hi Max,
That's one helluva question!
OK, so breaking it up...
I was wondering how the seo for an e-commerce site might compare to the seo for a blog or information based site
SEO is SEO, no matter what type of site you have, and the key is sticking with best practice at every step of the way. Aside from the issues the e-commerce sites send to fall foul of (duplication, cannibalisation, et al), then it is really just a case of making sure every 'i' is dotted and 't' is crossed. Your content on the site looks to be pretty unique, so you have this going for you. I haven't run a crawl on the site, so not sure if there are issues lurking beneath the hood or not. Keep a close eye on use of canonicals to help avoid duplication.
Should you try and rank for similar terms, the same generic terms, or complelty unique terms for the best seo? Or should every page try and rank for different terms,
Every page on the site needs to target its own unique phrase to avoid keyword duplication / cannibilisation and to ensure you don't have different pages trying to compete for the same phrases.
And how many keywords or search terms should I try and rank a particular product page for?
Just one per page. Keep it descriptive but remember to tag it with your brand. This will indicate to Google that you are focussed clearly on that phrase for that page. In the page itself, don't spam that phrase though. Make use of synonyms, explanations and tech specs where needed. Go all out on content as this will be one of your biggest winners.
How do I find out what are my best, most highly converting, most profitable keywords overtime for Google?
You can use the Google Keyword Planner or SEMrush to give you an idea on what you should target. There is a very good article here on MOZ that explains about undertaking Keyword Research and another here on Backlinko. Keyword Spy is another good one that is free with paid options, as is Keyword Eye.
My domain authority has decreased by 3 this week, this is the first time it has gone down since I started with Moz a few months back, can anyone explain why? And how this will affect the rankings ect, and how I can get it back up higher agian?
Start by reading how MOZ calculate these scores. But I suspect back-links are going to be the biggest factor here. Someone might chip in with more precise details on this.
**And for linking and brand mentions, what are the goals of this feature? Should I find my mentions and ask them to talk about us more and link to us properly? I'm not sure if this is right. **Should I be asking other websites to make links to our pages, or should it be organic?
Link building / Outreach / Link Acquisition - whatever you want to call it, it amounts to the same - getting a link from another site. The ideal solution here is look at your product and think who would be interested in this, then make contact with them.
Linkbuilding is a huge subject that I could write a small book on, but you need to keep it clean - don't beg for links and make sure a link has a good reason to be sat on another site, and never buy links - you will come unstuck.
And for the insights section, I am recieveing tons of issues a lot to do with duplicate content, will having the rel=carnocial tag fix these issues?
It should do, but without looking at the site myself, it's difficult to say with any certainty if this is all that is going on.
Hope this helps
-Andy