Hey Jeffrey,

So in general I wouldn't lose too much sleep over GWT 404 errors.  No matter how many I've fixed, a few pop up that I have no idea how Google landed on them.  The ones I'd worry about most are the ones that have links pointing to them, internal or external.  GWT should give you the referring page so check those out and fix them.

If there are a few that keep cropping up just 301 redirect them to another page.

You should take a look at the sitemap and if there are /feed/ URLs in there, remove them and resubmit.

Hope that helps,

Jacob

I think the two answers above pretty much cover it.

HX tags aren't a huge SEO factor so I wouldn't lose sleep over them.  Fashion your titles for users and if your page is about X Keyword.. GREAT  put that into the title naturally.  H1 is the only tag I wouldn't have more than one of.  H3+ could be duplicated on product titles and whatnot but again it isn't a huge SEO ranking factor anymore.

As far as font sizes I'd make them pleasing to the eye.  Google reads HX tags as they're intended to be used: Large titles at the top of the page in H1 are more relevant than multiple H3 tags with small text down lower etc.

Don't worry about making them "Exact match" so much as making them describe what is on the page.  Hopefully it happens to be describable with your keywords of value but having them make sense is the most important goal.

Hope that helps!

I don't think there is a solid YES/NO answer to this that you're wanting.

Not sure why you couldn't do one test since you're already concerened about the problem being present.  This would be the ultimate way to find out if your setup allows this.

It depends on if the user accepts cookies and whether you've configured your ecomm software to allow refreshes to trigger the GA code a second time.  USUALLY GA will only log one conversion per visit so you're probably okay.

Just dont take your data to be 100% accurate all the time because if not this particular problem it may be another.

TL;DR: Test it on your setup.