whatever your legal limit is, plant it. soon you'll figure out your sweet spots, work flow, storage needs, and weak lit areas, reduce plants or change up training to accommodate these needs. Only you know you'll train, how big your ass is, your plant pots, watering techniques, equipment footprints, etc.
Not sure about led lights, always wondered why the big producers are not using cobs, but they look promising to me.
grow tents make the most of your lights for sure, and rooms make the most of your plants, with options of placement and work space. Both have advantages over the other, its a personal choice. walls dont need mylar, but some plastic would be fine, to keep sprayed/splashed liquids from the wall surface. In a room I walk all the way around each plant, including the ones along a wall. I find the mylar wall plants perform no better/worse than the killz white wood plants wall on the other side of the room.This is what the room looks like. I have 8 fem seeds . If I grew 8 plants in here, would I need to build a grow tent or leave as is and just use the whole space and of course line the walls with mylar. Measuring from the end of the cabinet to door it's 4x8.