One is commonly allowed a stop on a domestic routing <4 hours, and <24 hours on an international routing before this is defined as a stopover. So, a west coast stop works on your trip to BKK: it's an international itinerary.

Yes, you can take advantage of the free domestic upgrades, but only where you have a change of flight number; watch out for the infamous 'direct flight with change of gauge' as they'll use that as an excuse not to upgrade you on the domestic segment.