Are you building the shed yourself?
If so, you might be able to incorporate a couple of deign tweaks to get around various problems that might arise from having a tank in the same area with rabbits.
What initially comes to mind is building the southern side as a greenhouse and using the 250 gallon tank as thermal mass as well as the fish tank.
As for the rabbits and humidity, I'm not sure about that, but once again if you're building the shed you can keep the rabbit cages separated from the aquaponics area.
Keep us informed, I'd like to see what you do with this project!