ima use that rack layout when i need to build a huge rack, cause i know i eventually will. what i though of already is to use a a t joint coming out of the bucket and running two different lines(one for the top couple racks and one ofr the bottom racks). thats just me cause i feel if you have one really long line its not going to be as effective as if you have two seperate lines of the same length. you could try that out.

and also i dont know the benefit of runing the water down first then winding it back up the rack system. i think it would put some extra un-needed "stress" on the watering system.