1911s have pretty poor mileage on their green gas (propane), due to the single stack mags being slimmer than a double stack mag, and thus not being able to hold as much gas between refills. That's another reason that some people resort to CO2.
CO2 generally shoots hotter as well, so keep that in mind when you're deciding on how many CO2 mags to buy. Generally CO2 pistols aren't used in CQB-only fields.
One last thing to consider, is that these pistols are made with crappy pot metal out of China/Taiwan, so additional force from CO2 can start causing you problems. I don't think you'll be going out to play pistol-only in -40 degrees, but cold pot metal is even more brittle than usual.
If you're a beginner, you may not be aware that these toys are pretty low quality for the amount of money you pay for them, and that's part of why people will always suggest that you "save up for a better one".
Let's say I bought a no-name Chinese game console for $200. I put in a disc, turn on the power, and then suddenly hear a grinding from inside. I open up the console and see that the disc drive was misaligned, and when the CD started spinning it caused the whole drive to start shredding the crappy internals. I'm now out $200, and since it's a crappy mass-produced console from a foreign company that doesn't do refunds or warranties, I'm also out of a console.
But if I had spent twice that and bought a decent console, then I would be significantly poorer, but at least I would have a console that works, instead of an expensive paperweight.
So with that said, it's pretty important that you have the right expectations for what you're putting your money into. KJW is a solid brand; the first pistol I ever bought was a KJW M9, and now several years - and thousands-and-thousands of shots later - it's still works as well as it did when it was brand new. But I also have a small bin with literally thousands of dollars (MSRP) worth of pistols (many of them KJW) that are broken and useless, and just used to salvage parts from.
I wouldn't start any "lower" than a KJW. Depending on the model of pistol, the two safest brands above that are KWA and Tokyo Marui. However, KWA and Tokyo Marui are far more respectful of trade marks (so for example, KWA has a training weapon that is "slightly different" than a glock, since they're not licensed), and TM only builds their stuff for the Japanese market, where the law says it has to shoot under 300FPS (I think) and be made of plastic. But the performance that you'll get out of a TM pistol is about as good as you'll get out of a stock pistol.
Other companies may have pistol models that are better than other models that they carry. For example, when it comes to glocks, KSC is pretty solid. Do not buy a KWC. (These brands get confusing, eh? KJW, KWA, KWC, KSC...)
You'll also want to make sure that you're maintaining your pistol half-decently. If you're leaving your mags dry, the o-rings will dry out, and you'll get a leak. If you don't lube your slide, you won't get good gas performance (and it may cause other problems), etc. Maintenance isn't complicated, but it's necessary.
So yeah, when you're making your purchase, don't expect it to last forever, and be aware that often "you get what you pay for" if you decide to go with a cheaper pistol. Also, if you're looking at WE pistols, make sure you know which version they are. WEs for a few years ago are absolute crap. And they haven't revamped their production/design on all of their models. I personally avoid WE, but as others have mentioned, their newer stuff is getting better.
Before you buy your pistol, make sure you hold it first, and like the feel of it. Most people have a list of pistols that don't feel comfortable in their hands. For example a 1911 grip may be too small for you, or an M9 grip may be too big, or a P226 may feel too vertical, or a MK23 may feel too unwieldy, etc.
You should also be aware of what replacement parts/brand compatibility are available, and how easy it is to get mags and holsters for the pistol. Most pistols are TM clones (meaning that Tokyo Marui made a pistol, and then companies in certain countries that disregard intellectual property will get their hands on it and make a crappy version of it for cheaper, but made out of pot metal and capable of shooting hotter, since they're not constrained by Japanese law). This means that "TM clones" are able to take most TM parts for the same pistol, so you should be able to get aftermarket parts for most TM clones.
Pistol models from companies like KJW and WE are usually TM clones, or at least TM compatible. However certain other companies, like KWA and KSC generally design their own systems, and are not TM compatible.
And then there's some companies who want to make pistol models that TM has not yet produced, and thus cannot be cloned. So they make their own models. WE does this a lot, and you may find that WE is the only company that makes a certain pistol model.
Sometimes you'll get lucky and find that the model is built with certain TM compatible aspects, while other times you'll find it's just some super-crappy proprietary system, with very little support from the manufacturer, nor any aftermarket parts producers.
I also mentioned checking what holsters are available for your pistol. There's different retention systems on holsters (SERPAs, Safariland's, Kydex, etc...Avoid a "universal" fabric holster at all costs!), so you should try and figure out what you like drawing from. If you don't have friends/game mates who have these holsters for you to try, just take a look on youtube to see how they work, and what people think of them. Keep in mind that in airsoft we're not too concerned with preventing someone else from taking our gun out of our holster, but we are concerned about crawling through the bush and finding out at the end of the day that our pistol fell out somewhere during the day.
The reason you should consider the holster, is because you want to make sure that your gun will fit the holster. Because these holsters are generally solid and unchangeable (unless you get a custom kydex holster molded to your gun), you may not find a holster for your gun. For example, Blackhawk does not manufacture SERPA holsters for an MK23, but an MK23 is a model from KWA that you can purchase. So now you know that if you want to use a SERPA holster, you would have to cross an MK23 off your list.
You should also take into account that certain airsoft pistol models from certain companies are not perfectly to spec. Certain companies that produce glocks, for example, are known to make them either too thick or too thin to fit in a real steel SERPA for that particular glock model.
Anyway, this has gotten much longer than I intended it to. I just wanted to say a couple lines about gas efficiency, and shooting CO2 in the cold, but then this opinionated-and-slightly-behind-the-times post spewed out.
Good luck with your pistol purchase.