You don't actually "renew" a visa, you apply for a new one, which means you can meet the financial requirements by using money in a US bank account. There are some changes afoot with regards to insurance so you'd need to check with the embassy on the requirements at the time you apply.
When you move to Bangkok, either the hotel, your landlord, or yourself will file a TM30 form. This effectively makes Bangkok Immigration your new port of call for immigration matters
Daniel Brm. The app is always working. I've used it about eight times in the last six months. But if you prefer to do it by mail follow Tod Daniel's instructions here
I'd advise your friend to register his place on the TM30 website or app, and then simply add you as a visitor. Each time you leave and return he can do the same. Trust me, it's much simpler