What kind of guns/kit will I need to start out? Face mask etc..
Decent boots with ankle support. Eye protection - polycarbonate safety glasses or goggles, or mesh, many options are available. Pyramex i-Force dual pane glasses are a reasonable default, or an Dye i4/i5 full face mask, or most stuff by Bolle or Valken or... (and on and on). You can add lower face mesh protection if you like, or just wrap a scarf round, or risk your teeth. That's it, you don't need camo or tacticool gear.
You need a defence to buy a RIF, but you can buy a two-tone without issues (as long as you're 18+). The site owner, marshals and players will keep you right about what to do with it. Some site will arrange for you to purchase a RIF that's send to them and essentially loaned to you on game days until you get your UKARA defence, but not all, and then it's still going to be passed around which kind of obviates the point of not doing rentals. However, since HQ Airsoft didn't mention this as an option, I suspect it'll be two-tone, or wait.
On a gun, pretty much any carbine/rifle sold by PatrolBase will do. I'm not suggesting buying from them, just that the range they stock represents stuff that works, down to the cheapest £80 CYMA M4. You don't need a pistol, and should avoid retailers with "BB" in the name unless you know exactly what you want from them and why. Even if your gun comes with a basic nihm battery, you'll generally want to buy some 7.4V lipo batteries, a decent charger (IMAX B6 variant) and think about magazines - you
can play with a single hi-cap, but many folk prefer to run multiple mid-caps.
Now, all that said, it's generally strongly recommended to rent first, but that doesn't seem to be an option at the moment, so you'll have to make a decision about whether to wait, or whether to dive in.
If you do, just don't go crazy, you can easily dump multiple hundreds of £££ only to find that it's not the experience you thought it would be. Yes, you can flog stuff on, but two-tone is harder to shift and "barely used" doesn't mean "barely depreciated".
Tough call right now, but I would encourage you to try and find a way to play, it's ace.