Welcome!
There are a good few sites in Essex though you'll likely have to come closer south.
I'd suggest taking a look at this site to find yourself a site to play at.
https://playairsoft.uk/map
This sticky topic is worth you having a butcher's.
Don't worry about going on your tod. The airsoft community is largely supportive and will be happy to help guide you on your first few games - the more you play, the more likely you'll play with and against the same people so there will be good camaraderie found soon enough. I get on really well with a fellow I more often than not play against.
In terms of gear, much of it will be a learning experience for you. Advice on what you equip will be hugely personal and you'll have to discover what works for you over time.
I'd say there are 3 key points when you plan getting started.
Don't skimp on eye protection. Absolutely do not buy it from Ali Express, Wish or Temu - you are playing a huge gamble with your eyesight that just isn't worth what little saving you will make. Even with Amazon and eBay, fakes are sold frequently. You're best off buying from an airsoft retailer where their supply chain will only give EN166 or Z87 compliant eye pro. You don't even have to spend huge amount of money. You can get perfectly suitable eye pro for under £20.
A decent pair of boots with ankle cover is recommended. You can walk on uneven terrain frequently or put your foot in a literal rabbit hole. They may not prevent you from breaking an ankle but they can help prevent less serious an injury.
You're best off doing rental rather than buying a gun to start with in case you decide it's not for you. You can buy a two-tone to get started but there is a consistent story where reselling it becomes very difficult and loses more money than expected. Some sites have their own shops so you can handle the RIFs available if they have them or it may be worth you visiting an airsoft shop to get that hands-on feel.
If you have any questions after you've done that reading, do let us know.