For the games I've worked on we have never used python in the actual game (for scripting we used Lua mostly) but I've had quite a bit of experience using it for tools and writing scripts to automate specific jobs.
It's a super awesome language and very handy to know.
I'm pretty sure the perforce merge tool is free to download on its own - P4merge. I have never had any problems with this and for c# files should be more than adequate. That's what I would go for if you want a free solution.
Yep Haps is right. Unless they've changed their procedure since last summer when I was messing around with it you need an internet connection, an xbox live gold account and something else which I presume is the AppHub membership that Haps said. I know I got a years worth of membership free from Dreamspark because I was a student if that helps but you still need the other things.
I would highly recommend GLFW, I just started using it recently having used GLUT all the time before and I really like it. It leaves your code clean and leaves you in control.
I only used GLUT before because that is what I was taught but now I realise it is outdated and a bit rubbish.