[BCOrchidGuy]

Dean the size of sump depends on the size of return pumps you go with and the size of bulkheads depends on how much water you want returned to the sump. A 500 gph return pump may lose a lot of head pressure when you are pumping it through an entire room but initially it still sucks a fair amount of water from the sump. If you are using this all for discus then you don't need a lot of water flow but the very smallest I would go with for returns is 1 inch pvc. The size and number of heaters depends on what the room temperature is, if the room temp is 70F and you want to raise it to 86F then you have to provide enough heaters to warm the tank volume by 16F. It may be easier to heat each individual tank rather than heat the sump water and then deal with cooling as its pumped through the room etc. As far as side by side or stacked tanks, I would go with side by side if you can, stacking tanks means keeping enough room between the bottom of the upper tank and the top of the lower tank to allow for working on both tanks with out banging your head PLUS you'll lose head pressure on your return pump if you go with stacked tanks.

Doug