I have a space in the basement around 11x5 allocated for a dark room. The sink will be about belly button height due to the drain.

1) Would you finish the interior or exterior of the studs?
2) I was going to use black sheet plastic for the ceiling in a small section about 1 foot wide due to shoddy construction of the exterior steps when my place was built 30 years ago. There's no flashing behind them and you used to be able to see the dirt. I have since foamed the truss holes but I think dampness may still sneak through.
3) Venting will be handled by an old heater inducer motor that is in place when I used to air brush in this space. I have since taken down the two walls.
4) The door I was going to make a frame and use blackout shade from the fabric store, or instead of the frame maybe just velcro all the way around.
5) And the biggest question, finding a good 4x5 enlarger. At the moment I have a Durst 601m that a guy at work gave me. Its like brand new and has both 35mm and 120 6x6 carriers. I thought about ordering the intrepid conversion but I would rather have something I don't need to disassemble to go take pictures.