Here's my two cents:
If you're trying to save money, a vert-fed 'cocker is an excellent buy and HPA is a good choice.
-My very first upgrade would be a decent barrel kit, with a good range of Inner Bore sizes. If you can't afford a kit, or a barrel that takes different sized inner sleeves then just buy one other barrel. You don't have to buy the most expensive, CP's seem to be a decent compromise between cost and quality (Hey Dan!). Since you're getting a Closed Bolt gun, your paint-to-barrel match is very important. The ball has to fit just tight enough to prevent the ball from rolling out of the barrel when you point your gun down, but it has to be loose enough that the paint doesn't break when you fire the gun. If I remember correctly, the stock 'cockers used to come with barrels that have an ID of about 0.89" or so, so if you're shooting normal sized paint (not supersmall stuff) a second barrel in the 0.92" range or so would probably help you out if you get large sized paint. How do you select a barrel if you don't know what the ID is? Bring your old barrel with you, and a stick squeegee to push paint through; and test paint. Find a ball that is hard to push through your old barrel, and see if it'll fall easily, almost dropping through without pushing through your prospective new barrel. Once you find a barrel that the fat ball drops easily but hangs up in your old barrel, then that probably should be your new barrel.
Colors are pretty, but I find that the barrels with the glossy, shiny, black finish tend to work the best if it's an aluminum barrel.
Everyone has their opinion on barrel length. If you play alot of inflateable fields then longer barrels work better, 14" or even 16" even if you play front. If you play alot of brushy fields, longer barrels also work better (you can push your barrel tip through the "junk" better so you can shoot). It took me a long time to convert from my 12" barrels...especially as my best barrel is a 12 incher (I waited while it was put together and best of all, I didn't have to pay for it
).
-for HPA, the non-adjustables are theoretically great. I just don't like the longer necks they usually have and the fact that they take CO2 bottle O-rings. For me, the longer neck means that you have to use a longer drop forward, which means that the bottle actually moves a little when you put pressure on it...but that's just a personal preference. Buy a pack of 10 or more bottle O-rings (the white kind) and tape or tie or attach in some way (sew into your bottle cover???) a spare O-ring or two to your gun. You don't know what a pisser it is to have the countdown start, have someone give his tank a last minute twist to make sure it's on tight, and then all of the sudden you hear a loud hissing sound as your teammate yells "crap, my O-ring just broke". The last time that happened, it was my backman. I told him to shut up and he's now hitting the 50, and he has 30 seconds to bunker someone before he runs out of air...he took out two guys
Always apply a little bit of lube to your O-ring before you screw in your tank, it'll last longer that way.
Another reason I don't like the non-adjustables is that when I got the first of my Intimidators, all the non-adjustables were in the 800 psi range and that tended to overstress my LP reg...meaning I'd have to change my LP O-rings every so often if I wanted my gun to stay consistent. Now of course they make non-adjustables in the 400 psi range, but if someone needs to borrow your tank...oh well, forget them, but non-adjustables are perfectly fine for people that don't mind the longer necks.
-Aside from an extra barrel or two an upgrade to think about for your 'cocker is a swing trigger (and eventually an e-blade when you can afford it). You don't really "NEED" the swing trigger, and you won't miss it if you never get it, but once you get one, you'll like it. If you can buy your 'cocker with one already installed and tweaked, so much the better...don't try removing any of the springs in a swing trigger in an attempt to lighten it up, trust me...
-All the other upgrades for a 'cocker really aren't needed if you don't have alot of money. I know the factory hates it, but I use my inline reg. to regulate my velocity (the factory wants you to use the velocity adjuster that the cocking rod passes through). I prefer to stay away from macro and mini lines...I like steel braid, but if you do decide to go with a plastic line, use the larger Macro line and always have spare line in your kit bag. The locking collar nicks the plastic and eventually causes a leak if you mess with the line alot, and no-one ever seems to have spare line when you really need it.
Just remember to match your barrel to your paint, and don't touch your gun for the first three months or so (have a professional do it for you if needed) until you get used to how it works and can read up on it, get a hopper that takes batteries, and you'll have alot of fun with your gun
Ray