I am fortunate to have an empty building (1000 sq ft?) with a massive crawsplace, working electric and faucet 30' away. The building is in excellent condition and is a steel roof on a concrete block wall and foundation. Used to be for raising pigs.

I want to raise fish and veggies as simply and cheaply as possible.
Fish: I think I can pull up the flooring against the deepest wall (southern) and drop two 300 galllon rubbermaid or IBC tanks below the outside soil surface (not much, maybe a 1' but the crawlspace is what will govern much of the temperature). This will insulate the fish tanks and keep them at near constant temperatures, regardless of outside temperatures (hot summers here which I'm concerned will drive down air saturations of the water). This probably rules out Tilapia as it will be too cool and heating the tanks will be painful as the heat will just get mostly rejected to the soil. However, I like catfish and think my family will, too, given the chance to raise them ourselves. There won't be any sun to grow algae and I'll be able to protect the tanks from predators (we have hawks, racoons, possums, etc). If anyone thinks a future option would be good, I can place styrofoam insulation underneath the tanks in case I ever decide to heat them. Will give me unlimited access to the fish (nothing above them) and I can put chicken wire over the tanks if the fish decide to jump. If I ever get really motivated I could floor it back in, resulting in no loss of barn sqft.

Veggies: Since this is all on the southern wall I can go outside the barn and build a support system, utilizing an existing concrete block outrigging. This will put the veggies up high, out of the reach of animals (family goats included) and yet give 100% of natural sunlight exposure. Disadvantage is that the veggies will be up high but I can build a ladder system and realistically, they are only 6' above the soil surface. Additionally, in the future I plan on enclosing this structure as a mini-greenhouse to lengthen the growing season. At first I am hoping to grow cucumbers and perhaps lettuce. We love black-seeded simpson lettuce! Once again, no loss of barn sqft.

Pump: Due to the height difference between the two (guess is 8') I would like to use a 1/5 hp sump pump. At zero head, it claims 25 gpm which should still provide a lot of flow at 8' of head. Advantage of the sump pump is reliability, cost, and the ability to pump up to 25' of head. Also easily replaceable/cheap so I could go ahead and order a spare to have on hand. Or better, wire in two with a timer to share run-time, giving me a lot of redundancy.

Misc: I feel comfortable drilling through the concrete wall to pass plumbing lines. I live in VA which has pretty moderate weather. Would like to use gravel as that is cheap. On well water so I have a cheap, near-limitless supply of good water. Doing it this way will give me a ton of grow-room for additional capacity.

Questions:
Does this sound doable?
Is the pump too powerful or is it good to have that much extra capacity? If too powerful, perhaps I can set it on a timer.
Recommendations?