Insulation for Bonus Room

I'm currently finishing out the 500 sqft bonus room above my garage. I'm doing as much of the work myself that I can (except for plumbing, hvac, elec, and sheetrock), but I'm not completely sure about how to go about the insulation.

I built the house with radiant OSB for the roof sheathing and the bonus room has a 5' knee wall surrounding its perimeter that slopes up to 9' ceilings at the top. There is some attic space above the 9' ceiling, but it will be inaccessible once the room is completed. The room sits on 16" i-joists with 1 1/4" subflooring. In between the joists there is some relatively thick (about 5") unfaced insulation that runs the length of the joists.

My current plan to insulate the space is the following:

1. Install faced R-13 around the knee wall with either tyvek house wrap or rigid foam board behind it to effectively seal out any air leakage from the attic space.
2. Install R-13 along the sloped roof portion, up to the flat ceiling. The rafters are 2x6 with 1.5" furring strips attached to their faces. Using the 3.5" R-13 inside the rafters will leave about 3.5" of unobstructed space for air flow.
3. Install R-38 in the ceiling joists of the room.
4. I'm unsure if I should leave the unfaced batting underneath the floor joists or just seal the open ends of each joist with rigid foam board, or even rolled up batting in a plastic bag. Some of the diagrams I've read online imply that there shouldn't be any insulation under the flooring and that you should completely block off the ends of each joist.

I've attached pics of the room as-is for reference. Any insight from others who've built out bonus rooms? I will be installing a 18k BTU Mitsubishi mini-split in the room for ac/heating.