How long do I stay in Thailand with a non-immigrant “O” marriage visa before it expires, and can I enter on a tourist visa thereafter?

Hello Thai visa group,

I get my non imm multi entry “O” marriage visa through Singapore and have done for a few years.

Couple of Q’s

1. Can anyone confirm how long I get in Thailand when I enter just before it expires ? I know that whatever allocation is given it cancels as soon as I leave the country again.

2. As a back up I would like to know if, once expired and I leave Thailand, could I re-enter on a tourist visa exempt 30 day ? Or would I not be deemed a tourist based in my visa history and family status ?

Thanks