Codeshares my friend - look for a Star Alliance or One World airline and most likely they will codeshare with partner airlines - if you can find that you will indeed have one ticket and one checkin for luggage
a month between SR and PP would be great - plenty to see and do to keep you occupied. Maybe not a month every year, but might depend on the friendships you make while you are there. In PP I suggest the Embassy Place Apartments - used to be Accor, maybe still is - lots of long stay residents who work in the embassies and are lovely people
there are 5 categories - most of them ask for a yearly income rather than a large lump sum.
But to your point: if you had $1m in a bank account where else would you choose to live ? One of the many things I love about this place is if you’re here on a budget it’s awesome, and if you’ve got some cash to splash it’s even more awesome
ltr.boi.go.th - there is a category of Long Term Resident Visa (10 years) designed for you - and a huge benefit is it won’t tax you on foreign sourced income
Sadly no - I am told Krungsri will bump you up to VIP level if you deposit THB5m and keep it there for a few days - that apparently allows you to open a safety box