One other thing to consider depends on your diffusion method. If you're using Atomic-style diffusers, I'd recommend either another rig or switching to all reactors. I've had a lot of difficulty trying to balance the pressure and needle valves for two Atomics, and was completely unable to balance 3 of them on the same rig.
On the other hand, if you're doing all reactors, no problem. And even those cheap needle valves will do the job, though better valves will make it a lot easier on you.