RiRxBr, I am very excited about your idea as I have lots of fish tanks. However, your diagram shows one small problem that should be addressed. Your fish tank air pump appears to be below the level of the water. This is a risky business, unless you have a one way valve (gang valve) in the line, as water can siphon its way back up the air line into the electric motor causing unwanted excitement to say the least, particularly if the power goes off. I realise that you don't want the power to go off anyway, but no sense in increasing the level of disaster likely if it does occur.
I have tried using a fish tank as a plant propagator and not had good results, using a very similar set up. The air temperature was clearly a fair bit lower than the water temperature. However, I must admit that I still had fish in the water at the time, and was reluctant to turn up the heat beyond 27C in case I cooked the fish. I think I could bring myself to relocate the fish to hatch baby chickies!