I got my t2i earlier this year and had some of the same questions as you do. The director I've been working with for the past year and a half gave me, to be what I consider to be, good advice for a cinematographer. I would tell him about this follow focus I wanted to get, or these monitors that were wireless or this really fancy rig I wanted and he would say, "get lenses!"
You said you wanted to get the 50mm 1.8, do it. It's a beautiful lens and when you have it wide open you get a really shallow depth of field, as well as it's only $120 or so.
As for rigs and such, build your own, or have someone who's good with tools to make you something. A friend of mine made me a pvc shoulder mount, I love it. It doesn't have rails or anything but it serves it's purpose of being a shoulder mount and it works great. And it cost him something like $25 to make.
I'm looking into making my own follow focus and perhaps adding on to my shoulder mount so that the follow focus attaches to it.
Gear is expensive, so invest in the stuff that lasts, get lenses.
You can have all the equipment in the world, but if you don't have lenses you can't shoot anything.
Hope that helps answer some questions for you.
