When you do find a suitable day:
Although not a competition, very few standard policies will cover a track day; special one-day policies are available I believe, but relatively expensive. Really it's up to you.
The standard seat belt will be fine. User your knees etc to jamb you in place in the corners.
Check check check, and check again EVERYTHING. Start with brakes, tyres (especially pressures), fluid levels, and anything that could fall off. You'll probably only do about 200 miles max. so 5mm of tyres will be OK. The car will roll more than a M-sport, but it will corner fine. Just take your time to get used to it. You may run out of brakes, especially if you stay out for more than 15 minutes at a time. If they fade, pull into the pits and let them cool off. You'll wear nothing out except yourself.
Other drivers? Good point. Listen carefully to the briefing and do whatever you're told. You'll probably be expected to use your mirrors and stay out of the way on straights.
On-board footage? Ask.
If you can get one of the organisers to go round with you, do it; it may cost.
Take your time, you've got all day. But most of all, enjoy yourself.