Im really looking forward to your SD grow and see how your res probs work out.
I will have a very similar setup.400W-3ftx3ftx6ft tent and hopefully DWC.I will buy the Neptunes 25L Buckets with 2L/m airpump.I wish the pump had more volume but I may buy a bigger one later.
A R/O with 190l/day cost 59euros here.for me its mandatory because the tap water has 0.8-0.9EC.You should get one,too.I dont believe its more expensive in the states.