Attic flooring questions

We've been doing some updating on our second floor, where all the kids sleep and play. I can share pics if anyone's interested, but it is just mainly some painting and a finished 10 year old girls bedroom. We have a 4x2 doorway into the attic. Not a ton of headroom in there since it follows the roofline, but my wife had the idea of making it a full height door and putting flooring down. This doesn’t have to be anything fancy. The idea for the finished product would be a roughly 4x8 space to put a small desk, some light fixture or a lamp, and additional storage. It would slope from 8 feet in height at the door, down to about 5 feet. I’ll add some framing and put either drywall or paneling for walls, and also add some insulation while I’m in there. Desk to the left, and shelving to the right, with about 4 feet of space in between. Basically she can walk in and sit down and have a quiet space to study and do school work.

Thinking .5 inch plywood as a subfloor, and we could come over that with some cheap laminate to finish it out or go with some 1x8 or 1x12 and paint it. Is that enough to hold the weight of a teenager and small furniture, or should I go thicker on the plywood? Working on 16 inch studs.

Also, on the door, this 4x2 has a basic header over it. I would be cutting out the stud there and putting in a new header and framing in the door. I’ve got an extra 24 inch door that we removed from another part of the house a few years ago that will work perfectly here. Anything I’m missing? Only removing the one stud above the header and replacing with a header at full door height.