thats not exactly high bio load, really its not even close
as for the height get the coils wrap them around a 3-4" piece of pvc, overlap one coil onto another, build it that tall, put the 4" in the outer tube, and fill that with bio balls.
you dont need 1cu ft of bioballs just fill it "full" and itll be fine
how you split that is really up to you, i prefere to keep the spliting parts external, there a little prone to cloging.