I'm new to flying around Asia and I've got 2 questions:

1. I'm booked on a Thai Airways flight SYD-BKK in Business Class arriving BKK at 10:00pm, then connecting to a United Airlines flight in Business departing for NRT at 6:50am. Will my checked bags go straight to the United flight or do I have to leave security in BKK and recheck them given the almost 9 hour layover? (I'm trying to avoid paying taxes leaving the airport).

2. Alternatively, if I changed my itinerary to connect in BKK to an Asiana flight instead (all on one ticket - SYD-BKK-ICN) and the layover was 1 hr and 30 min, is that enough time for the bags to make it given where the airlines are located in the airport and the fact that I would be changing airlines? I know they are both Star Alliance but not sure how it works logistically in BKK.

I would really appreciate any advice you could give regarding the operations at BKK and what is suggested. Thanks so much.