asking an American when opening a foreign bank account for their tax ID and proof of tax filing in the USA is perfectly normal and is required by every bank to satisfy their legal FATCA obligations.
AM is the UK moped class, not recognized in Thailand. You have a full motorcycle license anyway so the AM category is irrelevant. You can legally rent any size Thai scooter / bike with an IDP. Most Thai rental bikes are commonly 90cc - 350cc with most popular being 110-125cc scooters.