Well. Since I play with Hy, him and I would have fun with you :3
In order:
1) Yes
2) Yes
3) Depends on your specs. Depends on what you mean by a "hog". Depends on what you want to do in the background of gameplay. More details and I can answer.
4) Try this:
http://www.systemrequirementslab.com/referrer/srtest on that computer. Based on MY knowledge, I don't think that the graphics accelerated will do.
5) CS:S. Only way to go. Most people argue that 1.6 is for better people. I think 1.6 is crap. I've had it since the day it came out as a separate game and not a mod. I still vote CS:S.
6) Tweaks? Well if you google ways to increase FPS or look on FPSBanana.com for stuff, thats what I do. Take quality down, HDR off, Bloom off, make it so the chambers to show animation, stuff like that. My frames are easily 200+ then.
Hope this helps!