connection time in SIN
 

How much time to allow in between flights? Will arrive in SIN (SQ, from US). Will 1 hour layover be enough to take a Thai Air flight to BKK? If i take a later flight, I'll have 4 hours layover instead. Enough to do in SIN?

If your SQ flight arrives on time in SIN, and you've checked in for your connecting flight at your origin, you will make it. I believe you should be able to check in for your TG flight in the US since they're both *A. No need to clear Singapore immigration/customs. Just walk to the next gate. You will need to hop over from T2 to T1 although the buildings are connected. There is a Skytrain which links the terminals.

If you do take the later TG flight, I think there should be enough in SIN to keep you occupied - mini cinema, large flat screen TVs (showing CNN, BBC, ESPN, etc.) , duty free shopping, XBox, free internet access, swimming pool (have to pay for this).

Baggage transfer is fairly efficient and fast.
Your bags will make it with an hour's transfer time as well.

Should be fine, but note it is a deceptively long walk back to the gate (a good five mins, whereas it only seems like 2 when you deplane), and then you have to clear security, so don't dawdle in the shops and arrive five minutes before departure or you may be disappointed!