You technically can not apply while in Thailand. However, it is possible to cheat the process, you might get caught. Is it worth it to do that, since you would still need to leave the country and re-enter if you got the visa this way. Your best option is to travel to a neighboring country and apply there (either in person or via evisa depending on the embassy). These agencies are for the most part not that useful, as they can’t support the process, like they can with other visas, which can be done in county.
the two main ways (in my opinion) that foreigners are here are those on retirement visas, which require you to be 50 years and older and now those on DTV, which are remote workers, etc. you then have the teachers.
I believe so. My understanding is that all non Thais (unless you have a specific visa that says you don’t have to) are required to report every 90days. Not sure why people are so concerned though. First time in person, future times online