Insulate the whole thing well, at the very least 4" in the walls and floor and more in the ceiling. Space heat with a 3kw fan heater (protected from water splash) coupled to a thermostat. Corrugated perspex attached to the roof (for rainwater collection) and guttering to channel it into a rainwater butt. A ring main made from overflow pipe at ceiling level will provide you with all the air you need even if you have a small pump. I cannot envisage you wanting to build a pond in there so have small tanks at the top eg 14"x8"x8", then medium ones in the middle eg 18"x12"x12", then your larger ones on the bottom eg 36"x12"x12". If you are intending on breeding the provision will have to be made for hatching brineshrimp (lighting, air & temp control). Your worm cultures will also have to be taken into account. I made a shelf above the top level of tanks to accomodate my Grindal and Microworm cultures.
Hope this was of some help
Regards
BigC