Think long and hard about trying to invest in Thailand. Your money will make more in a simple certificate of deposit than you will here. Rental income can be very seasonal and liquidity is very low.
I think it was a marriage visa and there's plenty of rain to justify a short stay to "clean up affairs" after a marriage. Just need to be honest and open.
If you are going from a long term visa to a short term visa then you are probably suspect and they'll want more details. Not knowing your home country and your Thailand travel history makes it hard to offer any further advice.
Non-o based on retirement. "O" stand for other and there's a list of "other types". You want the one that is for over 50 based on retirement from the drop down selector.