I am worried that errors in the style of my Statement of Purpose (SOP) will count negatively toward me. By "errors" I mean choosing the wrong font, font size etc. My question: are there general styling guides and possibly word templates for SOP?
Statements of Purpose (SOP) are short -- a few hundred words, or 1,000 words at most. Nearly all style guides for simple documents feature serif fonts for the body -- Times Roman, 11pt or 12pt, or equivalent -- and larger sans-serif fonts for headers -- Helvetica 14pt bold, or similar. Single space between lines in a paragraph, and double space between paragraphs.
That is all you need.
Beyond this, please spend all your available time on writing and editing. Aim for the very highest quality writing in English. Aim for an SOP that was written by a native English speaker. For example, you could read your SOP aloud to three native English speakers and have them give you corrections to any word or sentence that did not sound right.
You seem to overvalue "style" and undervalue "content". That's a rookie mistake because it's easy to see for a reader if you've spent too much time on the style and not enough on the content.
My recommendation would be to use some standard style that is neither exciting nor boring and use your time to focus on the content. Certainly expressions like "can easily devataste a good SOP" are entirely unwarranted.
In mathematics, it is common for postdocs and graduating Ph.D. students who are applying for jobs to post their job materials on their websites: research statements, teaching statements, and the like. I am guessing this is also typical of other fields, and it gives a sense of what a community thinks an attractively formatted document looks like.
You might want to poke around the Internet and find and imitate some of these. That said, as long as you keep the formatting simple, easy to read, and not distracting, I think that is sufficient.
My friend, do not worry. As long as your SOP's styling makes it easy to read, without distracting the reader from the content of your essay, it will be fine.
It is natural for a person's anxiety level to increase at such a juncture as where you find yourself now. Don't worry about your anxiety... but do try to find some ways to deal with it. Get some exercise every day, and make sure you are eating in a healthy way.