The stock barrel is bad, better than a stock spyder/pirahna but still bad. I have two for mine, a Lapco Bigshot and a 32* Nightstix, the Nightstix is quieter and cheaper, the Bigshot though shots more accurate but it's a lot louder, I don't mind, I'm not a sound freak or anything. A friend has the 32* Precision 16' it's very nice and quiet but I find it kinda long for MY taste, he just loves it. CP's are nice too.
You can use any oil that won't eat the o-rings and will not thick under cold temperature, I use the good ol' 3-1, $1 for the little tin can
It's the one that my gf uses for her sewing machine.
I think the nicest way to lube your gun it's to disamble it and oil part by part, you can put a couple of drops in the asa too, but won't lube the bolt nice (wearing the body more quickly) and if you have the delrin bolt the oil will reach it more easily. I use white lithium for the valve, but that's just me, I like to use white lithium in everything I can.
go to 32ice.com and download the manual of your marker, you will need it. Mine didn't have one, maybe the newer models have.
1- New barrel
3- Nice drop forward (except in the R X it already has one) Psycho ballistics drop is sweet.
4- Delrin bolt
I use a 20onz in my Rebel X, but I will recommend a 16onz (short ones) with an smartparts on/off valve. Shorter tanks help you keep your marker closer to your body, especially with a PB drop forward, it balances to sweetly.
The best thing to get instead of the x-chamber and that you could get a small nitro tank preset 850, if you have the chance to get N2/Nitro fills go that way you won't regret it!