hey Tech,
nice start, the brainstorming kinda reminds me of my 'little' grow, which spawned a whole sub-room and A/C dedicated to the space in summer. details in my 1st thai log.
what started as a small cabinet turned into a stealth flowering room, 3ft wide, 8ft tall and 7ft deep, with useable floorspace 3x5ft and 8ft ceiling, cut 6in hole thru ceiling for vent to attic, and a 250W HPS, which im sure will be upgraded to 400w (possibly with added T5's vertically in the corners), in the coming weeks.

ur venting will help, but summer will be a challenge. u may need some a/c action nearby

IMO, u mentioned a larger closet nearby. THAT would be my flwr chamber. the one u have setup would be veg.

as to white and that lovely wood...

no to mylar. u'll get hot spots and burn the plants

I would feel bad painting that wood. can u afford that thin white sheeting? if so, get that instead so it can be removed to show that beautiful wood, sometime in the future.

thats all i have for now.

Good Luck on ur grow!:thumbsup:
i'll be watching