Alright, so this is what I did.
I treated the whole tank with aquarium salt. Then I read about the cory cats about 10 minutes after treating and removed them all to a 10 gallon sand bottom tank I hve five albino cory cats in. So there are eight corys in that tank, which will be temporary as that is too many; I will be putting the three back in the "infected" tank when they can be put in.
Then I took all the plants out and floated them in the top of my 5 gallon betta tank and the 10 gallon, removed all the betta fish and the gourami, put them in a large bucket with the treated tank water, a hollow log and a few fake plants to hide in.
Then I did a 100% water change in the tank, replanted the live plants, turned on the new heater and the filter. I added Cycle and conditioner to the new water, and two teaspoons of salt just for disinfectant (I'm pretty sure the plants can handle that much, and if not, I can always buy more plants).
This morning I emptied about 30% of the water in the bucket and re-added fresh, as well as two more scoops of salt (the bucket holds probably about 7 or 8 gallons of water).
No one else has died yet and the one with the fat tummy is actually starting to look closer to normal now.
How am I doing?
Oh, and the nitrite had no color at all but the ammonia did (0.1), should I just change my water more often in the future to keep the ammonia down? How much is too much? Apparently over-changing caused the bacteria bloom in the tank.