How's it going Nsky! I'm definitely interested in seeing your setup; might be able to get some good ideas from you. For power I'm just running off a plain wall outlet built into the space. It's where the fridge used to be, so It seemed the convenient thing to do. I'm not using a whole lot of power, since the lighting is primarily CFL and screw-in LED floodlights and I have a small desktop fan in there - not a whole major drain on a circuit. The top one runs 24/7, and the bottom one is on a timer. The major power drain is a space heater, but it's on a separate circuit. I have a couple small power bars, one for each outlet, although I should probably go with higher quality than dollar store hahaha. But the pots are placed inside plastic trays and the bottom power bar is up off the floor to avoid contact with water. The top part should be raised too; maybe I'll do that this evening. Glad you mentioned that.
As for reflectivity, I'd love to have some mylar, but I'm still in the beginning stages of growing and I'm on a budget, so once again, the dollar store came through for me. I got a couple emergency blankets and stapled them to the interior, and in the front part I have a piece doubled up which hangs inside the door/dummy wall (call it what you will) like a curtain.
Not shown here, because it's a new addition, is a sheet of 1/8" board that fits into a set of grooves made from molding when it's closed. It's not 100% lightproof yet, but I have no plants that are near flowering yet either, so I have a bit of time to spare. I have some black corrugated plastic that I close up gaps with here and there when I'm in the mood to work on it hahaha.
I have yet to put in some venting, so for now I just leave the door slightly open. The vent may be done with some dryer flex line. I think I have a piece of 3" laying around somewhere, but I have no plans on venting it outside.
Maybe some of what I've done can be of use to your setup. I don't know, but I hope my somewhat detailed description can do you good. It's always good to do a bit of brainstorming. Take care for now, and I'm eager to see some pictures of what you have done. I'll post some updates on here when I get the tools and equipment tidied up.