Licence is required. Day passes sometimes available (like at ShelbyFest). I'd suggest you get a a CAMS l2s licence; the annual fee can usually be offset with discounts on insurance I think - with Shannon's?
Harnesses not required. But as Steve says I recommend them. My race harness clips in and out yes. You don't need the passenger side. At least not yet.
Fire extinguisher required. 1kg.
Gloves required.
Boots recommended. Closed in and usually leather or fire resistant shoes are required, and it is hard to get shoes narrow enough to dance the pedals easily.
Suit not required. Maybe use Yakka overalls like I did last weekend :-) heavy cotton is fire resistant. Not fireproof though. I am going to progress to that later on. Also I was sick of everyone asking me to check their
oil, clean their windscreens, and "filler 'er up please".
Helmet required. I use my motorbike helmet, but if I didn't own one already I would buy a Hans compatible helmet with the Hans gear as well. Maybe next year.
All that advice I can give because I got a little trophy last weekend so now I'm a bonafide racer
Go to the CCCV site and check out the "Sup Regs" for last weekend's event. It tells you what the requirements are.