While I agree 100% with everyone elses advice and guidance, I am going to offer a different perspective. Being that you do not currently possess any gear, you are in an advantageous position. When you go out and play, ask the rental office if you can swap guns out. This way, you can utilize several different rifles. Try an M4, a G36, or any other rifle you want. This way you can experience its weight, its feel. Once you commit to a battle rifle, its not like you can just pass it right off and get something different. It may be a while before you can upgrade. Speaking of upgrades, research that as well. You will need to review the weapons sustainability as well as its ability to accommodate any mods you may want. Look at the internals of the rifle, what version gearbox, what type of gear box, will the gear box need to be replaced quickly, what is the gear box made of, look at types of batteries. The last thing you want is to get the rifle then need to spend a chunk getting it up to spec.
As to gear, well again, thats personal preference. I do not know if its the same here in the UK as it is in the US, but most US players gradually evolve into a role they portray. You may want to run the same loadout as the SAS, or British Marine, GSG9, US Army Ranger/SEAL/ODA, Russian Spetsnaz. Heck you may want to portray Johnny Jihad and run around with a man dress on and head scarf yelling "DURKA DURKA JIHAD" while firing your weapon blindly over you head sideways. Personally I don't recommend that, but I will not discourage you if thats what you want. As you research your chosen airsoft persona, look at all the gear needed. Some units run light and fast, while others are heavier. I personally run a heavier kit, but I have everything thing I need for any situation. Its big, its bulky, it can at times make me a bullet magnet, but its the same loadout I used in Iraq. You need to find your style. RESEARCH RESEARCH RESEARCH
Above all else, do what will make you happy. Play the way you want. This is your hobby, and most importantly, your money. Go with what makes you happy.
~~~GARRY OWEN~~~