Guns are always personal preference, once you have a model in mind then its down to price range. baring in mind that for starters you will need extras: a battery(poss even a spare). Magazines. foregrip, sling, sights etc can be saved for later. you will need some ammo but that can be bought at the site on the day. a case to carry it in is always nice.
Clothing is also personal, but i would suggest a good pair of boots to support your ankle.
Btw have you ever been airsofting and are you familiar with the UKVCRA and UKARA?