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Hi, for building regs if you are following them, the floor of the crawl space must be insulated as it is the roof of the room below. Without this the room below will end up with mould on the ceiling and you will feel alot of heatloss. I’d recommend installing tile vents at high level and eaves tray vents at low level in the crawl space as you must ensure the crawl space is still well ventilated as it’s a cold roof design. If it’s not ventilated then you will get condensation in the loft area and timber rot.
The stud walls to the crawl space should be insulated too. You should have draughtproofing strips all around the doors to the crawl space.
Get an electric heater in the loft room and have it on twice a day for an hour each, you need to heat the air to take moisture out the room, then ensure you have window trickle vents open or extractor fans running to remove this moisture laden air. To stop mould you need heating, ventilation and extraction. Don’t decorate the rooms until the mould is gone and under control.