I have been at SJU in the middle of the night on more than one occasion. Not much open, but a lot of people wandering around. 3 hr layover will not kill you. Had many 8+ hour layovers.
What's wrong with Caribbean Sun? There are a lot of small airlines flying around down there. some have been there a very long time.
I have flown on Caribbean Star AL(I do not know why 2 airlines owned by the same guy) a couple of times. One time, the pilot came out to move some people from the back of the plane to the front. It was the president of the company. his picture was in the little magazine in the seat pocket.
They fly dash 8's which are very nice short hop airplanes.