Anything that slows down the bots or loading is a negative... How much of a negative depends on how slow you get... from a bit slower to a complete stop slow.

In addition, some of the templates have important stuff, like title and h1 appear in line 427... They'd be more helpful on line 68, for instance.

Caveat: I don't code, don't build sites from scratch... These are things I've noticed playing with various wordpress sites... Some of what I noticed may have had a different cause than what I thought.

So, ask a website builder / coder with experience if my observations are accurate.

That depends entirely on what you consider garbage. If there's more markup than you'd need to get a bare minimum website rendered that's probably not going to hurt you. I don't want to code from scratch because I'd need to handle all sort of silly beginner stuff, probably solve some basic issues in browser compatibility, etc.

If the site structure is weird, or there's a lot of code that's against the HTML specs, that's something I would look into.

If the theme is loading a dozen CSS files and a bunch of JS on the top of that, that's something you should investigate. There's tools that can combine the files, and this might not be a deal breaker for me.

Useless links tend to be bad for SEO.

In my opinion the content should be readable even from the source. There's of course HTML tags, but it should not be too scattered or too low in the structure (after something that's not important).

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