If you're like most people who get into airsoft, you'll probably end up trying a few different things before settling on something you are happy with. What works for one person, someone else might hate, and it often takes a bit of experimentation to find out what suits you best. Some of that ends up being down to your style, i.e. you might like running about all over the place, or you might like sneaking about, possibly both, you might like shotguns, or full auto machine guns, pistols or whatever.
That's why it's not a bad idea to rent stuff first. You'll get to see what everyone else who goes regularly is using and how useful (or not useful) their choices are when it actually comes to a fight. You can quiz people about their choices, and you'll find out what kind of player you are in terms of the way you play goes, and then be able to make a more informed choice without having spent money on something which you end up not wanting to use, or cannot get along with for one reason or another. That goes for clothing, boots, webbing/tactical vests, helmets etc, just as much as it does for weaponry.
For example, obviously you need eye protection, and if you hire it, the chances are it will be a full face mask. This is because, since airsoft sites have to ensure anyone under the age of eighteen wears full face protection, it's just easier for their rental gear to be a full face mask. However, full face masks can be a bit of a pain in the arse in practice, because they are often bulky and can end up preventing you from getting a rifle up into your cheek to use the sights properly, but there are things you can do about that. Some people will go with simply wearing shooting glasses and nothing else (risky, since it offers minimal protection), some people will go with perspex goggles (which can fog up but offer good visibility when they are not fogged up), some with mesh goggles (which don't fog up but are not quite as good in the visibility they offer), some will combine that with a lower face mask of either plastic or mesh, and some might use a shemagh or other type of scarf on their lower face. There are pros and cons to all of those things, for example, if you had an M16 with an optical sight mounted on the carry handle, you'd probably be able to get that up to your eye even with a bulky mask on, but you might have a different rifle which doesn't make that quite so easy, so you might forego lower face protection in favour of practicality, but then you are risking getting a tooth shot out (that happens sometimes with people who don't wear lower face protection and is why under eighteen players have to do so).
The more you can find out about what you like and don't like before spending a lot of money on gear, by just renting some stuff for a skirmish or two, the happier you'll be with what you ultimately end up deciding upon, and almost certainly better off money wise as well, in avoiding buying something you later find out you don't like that much. You'll make the odd mistake with things you buy, everyone does, but if you rent stuff first and get a bit more clued up about things, you'll certainly make smarter buying choices in general.
However, some things are going to be obvious from the get go if you are inclined to want to gather some gear right now, and in fact, you might have some or all of this stuff anyway, which is just as well, because none of this stuff will be part of a hire package: Some decent boots from an army surplus place will serve you well and won't cost much, and you definitely need good ankle support when running and diving about all over the place. Some combat pants will also serve you well, since they have pockets which are designed to be big enough to fit spare magazines in, but they are not the warmest attire known to man, so some long johns or cycling leggings underneath them will not only keep you warmer, but also stop hits to your legs stinging so much. A baseball cap (which everyone has anyway) will protect your forehead from BB hits whilst you decide if you want to have a helmet or something more specialised (trust me, hits to the forehead hurt and will bleed, so cover it up, because hits to the head are very common). Some thin gloves will offer some hand protection from hits, but will still let you operate your weapon properly (hits to the hands and arms are very common too, so again, wearing long sleeved stuff and gloves will minimise that stinging, which it does, especially in cold weather). A decent scarf, such as an Arabic keffiyah (shemagh) is a good buy if you don't have one, since it will protect your neck from hits, if you do buy one, get an olive drab one, the more typical white ones stick out like a sore thumb in woodland terrain. Hits to the neck hurt and can draw blood, which is why you see so many players wearing those scarves. A small water bottle is a good thing to take with you too, since you will get thirsty running about shooting people.
