I have a 100 year old house, upstairs attic has electrical service and I can run plumbing to the space as well. Have floor insulated and plywood, and framing done. It's a peak roof, so there is limited headroom along the sides, but I need to know the best way to properly ventilate and then insulate, before I proceed.

You can put the ventilators, screened or louvered opening in the end walls under the peak of the roof. The vents should be between the roof and the insulation. You can put in a knee wall at the low headroom ends of the sloping roof and a dropped ceiling over the peak. Then staple rolls of insulation in between the rafters. Dormer windows maybe, unless there are already windows in the end walls

Insulating the floor only is helpful from the point of view that you kill some noise between floors you do nothing for the temp of the room. Your knee walls need a vapor barrier facing the warm side. You roof rafters need to be left nearly completely open since you must allow air to rise in each bay so do not push insulation right up againist the underside of the roof, leave a 6 inch gap. I'd lower the ceiling so you can get at least R33 insulation in your ceiling, where do you live?