With a ceiling that high, I'd go with the longer drop. A 72-inch rod puts the blades around 8 feet 9 inches off the floor, which is right in the sweet spot for moving air where you actually sit, and it keeps the fan well clear of the sloped ceiling. The 48-inch rod would leave it up around 10 feet 9 inches, which is a bit high to feel much breeze down at couch level. Just make sure to use the manufacturer's own rod and the sloped-ceiling mount that came with the fan, and check that the blades will clear the ceiling and the crown molding as they spin. If you can, have someone hold the fan at that height on a ladder first and check the look and the clearance before you wire it in.

go 72. blades around 8'9" basically line up with that 9' crown, so it reads intentional instead of floating randomly. one thing though, you've got an open loft railing right there, so stand up top and make sure the fan isn't sitting at eye level from the landing. on a slope that steep, have an electrician confirm the box is fan-rated and braced for that rod length.

Yes, select a 82" downrod, however, the size and style if the current fan is not one I'd retain. Select a white fan without a light, with a larger diameter for better air movement.