The thing to grasp is that right now you don't know much, so whatever decisions you make are based mainly on guesswork. Have a look on fleabay for something cheap that will do the trick for now and, when you do know more, like what kind of role you find most enjoyable, you'll be able to choose something with exactly what you need.
You can get surplus army gear for £20 or less delivered if you're a little patient: PLCE, Web-tex vests, Northern Ireland crossed strap chest rigs... or there's always the good old South African style vest which come in every shade of camo imaginable, but are somewhat more limited than some in what type of mags will fit in the ammo pouches.
If you think that lightweight and ammo only will do you, you might want to consider
US Army Enhanced Load Bearing Vest (LBV) - they come in US Woodland, Tri-Color Desert, Olive Drab & Black, that I've seen, maybe more colours, and hold 6 NATO mags and 2 grenades (or put whatever u like in the 2 small pouches).
What's your AEG?