I’ve been working towards a ‘book of style’ for my own sites for years. I usually just refer to one of the online print publications like the Chicago Tribune or New York Times. I do have some thoughts on the style I like and prefer after writing online for the last thirty years.
Over the last few years, I’ve made use of Grammarly so I defer to its interpretations of grammar and spelling.
For layout I accept whatever my current theme for any given site provides or else modify that theme to suit my own sense of style there.
My suggestion would be for you to adhere to something as above and chose themes that either provide the layout you desire or else modify that theme to do so. One caution might be to always use Child Themes when modifying themes.
Writing and language grows over time. Styles change but your readers will appreciate your consistency. Your style should reflect your personality somewhat also. As I get older I’m more set in my ways and I still ‘smart’ from some remarks made years ago about my own poor grammar. Learn from that and grow should the same happen to you.
As an example, I’ve read and reread these few paragraphs several times while my tools have alerted on grammar, punctuation, and spelling. Don’t be surprised to see an edit note on this after I publish it here also.
You might also note my use of the Oxford (Cambridge or serial) Comma in the paragraph above. And yet I’ll often abandon those conventions… Willy Nilly.
I hope this helps.