Clothes: as has been said, the eclipse range are very durable and comfy, and go quite cheaply on the forums due to their popularity. Get pants before jersey, as a jersey will have less impact on your comfort while playing. I also recommend Dye or JT pants.
Hopper: This is an important piece of kit, as kitty has pointed out. If you're playing in the woods mainly, battery life will be of importance to you so I'd recommend an empire reloader B/B2 for a cheap but decent loader, or if you're playing speedball Vlocities are great loaders (battery life isn't as good though, but they are very light and go for a reasonable price).
Bottle: Carbon fibre are lighter and hold higher pressure (and hence more air), but they're expensive. If you just want to get up and running, get a steelie (around £45) and start putting aside cash for when you can afford a carbon fibre. It does make a big difference having a light bottle though.
marker: I would steer clear of the spyder. The vibe feels like something Tesco would make, but as far as beginner markers go: it shoots reliably and will get you going until you actually NEED a better marker. Since it's pretty far down your list and you might have a bit more experience by then, it might be worth saving a tiny bit more and getting an etek1 2nd hand for around the £150 mark. Excellent marker, very easy to maintain, you won't feel the need to upgrade it, I really can't do anything but sing its praises as a marker for the dedicated newbie.
Pack and masks have been covered already: NXE pack, and proflex.