I'm also planning to run nitrous with my car. The first thing I did was get rid of my dual plane intake and 4 hole spacer, and replaced it with a single plane and open spacer. I know some people run it with a dual plane, but if you think about how the wet system works I think some fuel would puddle on the inside walls of the intake. Scares me to think of a lean condition because of lost fuel in the plenum are. I may be wrong, but I like to be safe.
You said you are running an intake with 4 holes. I suggest finding someone who has done this or calling NOS (or equiv.) technical support and see what they suggest.

I guess if you are going to run direct port nos you can disregard what I just said.