3K USD?
it seems a good deal. If you can, try and get the BKK to FRA on TG connecting with FRA to EWR on AI. It seems like a nice combination. It would be a good comparison of AI and TG.
with my basic understanding, unlimited stopovers mean you can stop in FRA for a few days if you like and then continue onwards. Many one way tickets have no/or minimum restrictions, i bet you the fare is probably refundable as well.