I kept redclaw and western blues in fish tanks. You need a lot of cover on the bottom - old pots, pipes etc. When they shed they put out a hormone that sends the others into a feeding frenzy so the soft shell ones have to be able to hide away.
You will also need a cover on your tank. They are surprisingly good at going walk about and can climb like nobody's business.
Otherwise, they are pretty hardy, if somewhat dirty (not going to be a big issue in aquaponics). They are certainly easier than fish.
I've heard that walking through the rainforest near the water where the crays live, hikers find crays waltzing about on the paths so they are keen walkers it seems!
I have Red Claw crayfish currently and they are great fun to have in the aquaponics. I keep them in the sump, separate from the jade perch. Apparently really tasty too, though I haven't tried them.
Andy is right about their proclivity to escape. I don't have a proper overflow system, and I have lost a few in the heavy rains we've had. However, I have been lucky enough to rescue a few from time to time, as they've been walking down the street! It's a funny sight indeed.
Keeping them in the sump is a great idea mate.
thanks everyone for the advice will definitely take it all in when the planning is complete ...