Compare Wise and western union. Historically Wise (formerly transferwise) was cheaper but I just compared one myself and western union was a bit cheaper.
It may be been an option, but its not a requirement. to register a vehicle in your name you need to show residency. The DLT allows forigners to do this one of 3 ways, yellow book, work permit with address, or certificate of residency from immigration or your embassy.
It's possible information was either not correctly communicated to you, or the sales staff was not familiar with selling to forigners.
Yes you can, as long as your IDP is endorsed for motorcycles.
Also, prepare for a ton of old people to start yelling about how dangerous the roads are in Thailand, how 1 million people a day die from motorbike accidents, you'll be automatically responsible for any accident that occurs even if your not involved, and health insurance. Oh they love to moan about health insurance.