Grow room with an area of constant light and a lightproof area to do 12 hours of dark

I am trying to get the most use out of a limited budget getting a room started with some perpetual growth. I know to flower the plant on 12/12 so would it be best if I had seedlings and veg plants under light and then plants I was ready to flower I start in a cycle of moving those to a completely dark room for 12 hours a day? Same effect essentially for the flowering plants I would assume. Has anyone done this? Also my dark room will have enough room to flower 4 plants at once. My lit area would be about 4 foot x 4 foot. Is this enough space to veg 8-10 plants at once (half being seedlings and half being veg) ?

Doing that I would not swap out my lamp for Metal Halide to HPS in flowering? I was thinking running constant HPS through all growth. Would it have that much difference because of not enough blue spectrum?

Would it make more sense to have a 4x4 with the metal halide lamp and the dark room have a timer for the HPS when flowering?

I hope this all makes sense. Thanks in advance for the help!

Plants don't care what room they're in as long as the lighting is consistent. Good idea.
4x4 is awful small for veg and flower. Think about a narrow shelf high up for clones with a 2ft. fleuro fixture over it. Then mom and veggers can be underneath and not take up as much room.
Plants in this scenario can't be very big. Maybe veg to 12in, should finish at about 24in. If you don't top em, you may get 6 in there for a total of 13 plus clones.
Another option would be to scrog the 4x4 and keep the mother in a closet with some CFL's over her and clones on a shelf. They would only have to be in the closet till well rooted plus a week and could finish veggin as you weave em into the screen.
Btw, I use HPS in veg, seems to work ok.
Hope this helps
Fred