You can go a week before and some days after- not sure how many. The TM 30 check in is to the side of the main building usually very fast. The form is in the waiting area
All is long stay visas are 1900 baht you’re required to have money in the bank differing depending on the reason to stay … retirement…. Marriage …priesthood educational. There are agencies that can provide with the correct stamps probably 20/
No it isn’t worth the hassle. There are heaps of secondhand bike dealers in Thailand. It easy to buy register and insure… and apply for a driving license. It’s worthwhile doing all those things as you will be stopped for sure. That can get expensive!.