When you say you could deposit a couple of million, I presume you mean baht. Don't do it until this tax thing is clearer. Even then I'd only deposit the amount required to get the visa. 800,000 baht. Actually you need to get advice by the expat experts because there's several things you need to know before you make a decision. The guy that seems to be really knowledgeable is called Tid Daniels, just search him on FB and message him, he's very obliging with advice.
Any bank could close an account in the UK if there is no activity for a long period of time. I had HSBC accounts, Hong Kong, Singapore and then UK. Never had any problems.
So if you enter on 60 day exempt and have a return ticket for 90 days, the immigration are aware you can get a 30 day extension from immigration while in Thailand, so therefore should not stop you entering.
I used to do every thirty days, sometimes for a few months when work was scarce. Never got questioned and I used to border bounces everytime. It wasn't until ten years after I moved to Thailand that I got Red stamped. So did ok. Still let me in for thirty days, so went back to my country and got a non O multiple entry.