Sounds like your plan is coming together. Don't know of anyone using black crappie in aquaponics - I considered it going in but don't remember what made me decide against them - possibly it was that they don't take feed as well as other fish. I went with Channel Catfish and Bluegill - killed almost all my catfish right off the bat with too much nitrite - not cycled up enough. Going with native fish eliminates the need to heat or cool your water, as you probably know. Good luck.
black crappie are hard to get on feed.. it can be done, but it's lots of work
With just an IBC as fish tank you will want to do a bit to mitigate temperature swings from day-night during strange hot days to really cold night seasons. I would say you want to do this by making sure the greenhouse can really open up during hot weather since if it's 95 outdoors it could easily be over 120 in the greenhouse and your plants will be suffering if you can't shade and ventilate the greenhouse very well.