Chiang Mai, Bangkok, Buriram, Chiang Rai and a couple of others all allow people to apply for extensions when they have 45 days or less left on their current stamp. The other immigration offices are 30 days. However, ask your local immigration office for specific details.
Great question. The answer (to my knowledge) is yes - BUT confirm with the elite visa people.
You can have an Elite Visa, and when you're employed, you can have the Elite Visa "suspended", where you're legally on the Non-B visa/ Extension of stay based on employment. However, when the Elite Visa is "suspended", it is still "counting down" and will expire as normal.
Again, confirm with the Elite Visa people on that.
for the immigration offices in Bangkok, sometimes it's asked, sometimes it's not asked, and I can't figure out when it's asked and not asked 🙁 Bring it with you just in case.
TM30 must be submitted no later then one business day after you arrive. Your hotel or property owner should have submitted it. The approved TM30 looks like one of these three documents below.
The 90 day report varies depending on the immigration office. Some don't require it, some do. Bangkok Immigration sometimes require it, and other times it doesn't. I recommend going to Muang Thong Thani, Counter A, and ask them if you need to do a 90 day report.
Counter A does the 90 day reports, and would be able to give you the answer.