Upvote:3
If this is booked on a single ticket you will only go through customs and immigration in BKK and your bags will go all the way from SNA to BKK
If these are two separate tickets, you have a big problem and should rebook.
SNA to SEA is a domestic flight. 90 minutes is plenty provided your first flight is not excessively delayed. SEA to NRT is international but the US has no exit controls and you will not enter Japan but stay in the transit area in NRT. The first time you actually enter a different country will be in BKK>