Well....
it looks good so far....
a few concerns though:
1) Ventilation - Since you need to be constantly circulating the air in and out of the grow room, how do you propose doing this? With your cabinet idea it would've been pretty simple. Except that for the fact that now you really only can mount the fans to your cardboard door / wall. Which, once wet, will have 0 durability. Are you planning on cutting into the ceiling and installing a vent? Which leads me to ask, if you vent in on the bottom, and out on the top (basic thermodynamics, hot air rises), where would you mount on the bottom? and where on the top?
2) Security - I would highly suggest installing a lock on that door. If anyone asks, tell them you have valuables in there that you want to keep secure. It'd be one thing to open the closet and just see a storage cabinet in there, it's another to be greeted with a wall of cardboard with a 'door' on it.
3) You said you may plan on switching out the CFL's for possibly a different light (MH/HPS)? Just remember, the amount of heat thrown off by a MH/HPS in that small of a space is goign to be huge. Most likely will raise the temp. of the grow room significantly. If I were you, before investing anymore time or energy into this project, I would do this:
Get your CFL Lights. Your proposed fans / ventilation, set those up. If you also want to test for smell, get some type of air freshener or something. Set it all up as if you're actually using the grow room. Let it run for like 24 hours and check the temp / humidity inside of the room. Also be sure that the air isn't stale. Plants don't do so well with stale air. Remember your ideal growing temp is around 75 degrees. Oh and if you're going to have a MH/HPS setup in there eventually, that light must be air cooled as well....
Hope that helps ya some.