Traveling to Thailand, immigration and customs checks 3 times?

If this is booked on a single ticket, you will only go through customs and immigration to BKK and your luggage will go from SNA to BKK

If these are two separate tickets, you have a big problem and you should book again.

SNA to SEA is an internal flight. 90 minutes is sufficient provided that your first flight is not excessively delayed. SEA to NRT is international but the US does not have exit control and you will not enter Japan but will stay in the transit zone in NRT. The first time you actually enter another country will be at BKK>