You'll be fine, don't worry about it. If you need peace of mind, book a dummy ticket from an onward ticket website. For stamp extention you may need to wait until 45 or 30 days remaining instead of doing it immediately.
Not sure if "need" to. But probably should provide confirmation of business/tax registration. Most people report submitting it. But if you reply without it and the embassy wants it, they'll ask for further documents. Of course, this will extend the process.
As for other documents (not mentioned in your post), I would draft a cover letter briefly explaining your business, self-employed status, and remote nature of the work.
Regarding proof of location, you'll want to provide both entry/visa stamp and proof of accomodation (e.g. booking confirmation)
doesn't matter if there's official limit. They'll eventually pull you aside and say next time you need a visa. That's when it's time to get a visa 🤣
reason to get the visa is if you already have a recent history of a lot of visa exemptions, and it seems you're trying to live in Thailand off them, as many immigration officers have been "cracking down" more recently
Write a cover letter with the explanation you just gave regarding your business and self-employed status, and attach 1-2 sample contracts and perhaps invoices. If concerned about confidentiality, can redact client names. Also consider attaching business registration document as this seems to be asked for. Compile all as a single pdf to submit as only one document can be uploaded per question (at least during initial application).