To best answer this - we would need the dimension of the tank ! The volume is irrelevant.
No you should not 2 bearded dragons should be put in at least a 75 gallon tank. You could put them in a 55 gallon tank but they would be extremely stressed out.
either a 15 gallon tank or a 20 gallon tank
you can put a betta in a 5 gallon tank
you can put a betta in a 54 gallon tank
No less than a 55 gallon tank.
guppys are tropical fish. they require a heater, and 1 gallon is to small for a heater
A 1 gallon tank could have one betta fish, but you will need to be diligent about changing the water on a regular basis. The smallest tank that should be used, even for a betta, is a 2.5 gallon tank as it at least gives the fish swimming room.
you could put about 30,assuming they are all compatible
It depends how big your bowl is if it is below 5 gallons then you should put one. But if it is 1 or 2 gallons then you will have to move it into a 5 gallon tank or bowl at the least.
You can put it on a table if you choose. NEVER put a tank on the floor.
Remove the sick fish..... the fish that has the ich should be put in a hospital tank then treated for ich, corals do not get ich, only the fish, so a ten gallon tank with a aerator would be ideal for a hospital tank....
Drain the tank and do not run the engine until you refill it with diesel. The residual gas should not be an issue once the tank has been drained.