You might want to think about getting a Non-OA visa which gives you a straight 12 month multi entry visa. You get this from the consulate in your home country but it does require background check, insurance, etc
Show them a current receipt for something you purchased today, preferably with your name on it. If it doesn't have your name take a selfie of you holding it with a recognisable landmark in the bank and make sure the date is visible. You need to stay in Indonesia until the visa is approved
There's no definite time, entirely up to the immigration officer you will stand in front of. If he thinks you are abusing the visa exempt system he can deny you entry
an entry stamp from your passport, a receipt from today with your name on it. I would send both. And you better hope the visa is issued before you leave
If you are inside Thailand for 90 consecutive days you are obliged to report. The grace period only applies to the report not the number of days inside Thailand