Like the others have said 1/2 should work fine. But I'd be more concerned with humidity and do everything I could possibly do to prevent condensate and control it because you are going to get plenty even with an inline drier.
Getting the compressed air to cool in the plumbed line before the drier has worked for me. I have used schedule 80 PVC, cheap and rated at 690psi.
So volume in the line is your friend in the main lines. I know you said you have limited wall space but try and get creative and see what you can do.
I also didn't notice that the drops have any short drops w/bleeders under the couplers. Try to get this feature included.