Anonymous participant 237 Tod is correct, if you're on an extension of stay and you leave without a re-entry permit as soon as you leave it's no longer valid, nothing to cancel.
You are starting a business so you'll need a thai person to do that anyway, deposit into thier account to open the business, after opening the biz then they can open the biz bank account, don't know your biz but if you intend do anything online setting up stripe paypal etc at lot easier for the Thai national to do anyway
Anonymous participant 407 not really mate, the Thai Cultural Exchange is accepted everywhere cause it's a 5byear program and is designed specifically for soft power, a muay thai course is six months and could lead u problems down the road