Some other great places to visit: Pine Island Nursery, Excalibur Nursery, Kampong (Fairchild's historical home and orchard, you need appointment), Chapman USDA experimental station (also need appointment), TARS. Lara's is great, especially for info on mamey sapote. If you like mangos seems like Harry's place would also be obligatory. Suggest looking up old thread about best places to visit in Florida. It has more interesting places, addresses, maps, and more specific info.
This time of the year in Bangkok is probably lowest fruit season, but you should still find plenty all around to keep you happy. Have a great trip!
PS have you considered side trip to Sarawak or Brunei from Bangkok? This time of year is the best there for rare species of durio and lots of others.