Book your return flight for the 90 days and then go online and book the cheapest ticket out of Thailand within 60 days. You don’t need to use this ticket but it’s just there incase you are asked. Probably cost you £20 but worth it for peace of mind. You will then get a 60 day stamp when you arrive and then you can extend by a further 30 days
I know many people that use short term addresses to open the account so they can start to season the funds whilst looking for long term accommodation. Completely up to Mike which way he wants to do it but he seems like he has a solid plan