Advice needed: Looking at building a Linux Ubuntu home server with XBMC as front end.

[BrooksyX]

So I am in the process in trying to build just a small home server and want to base it on linux, most likely ubuntu/ubuntu server. I have access to a copy of windows 7 or windows server 2008 r2 through my college but I prefer the light weight of linux and free applications to use on it.

First of here is hardware I will be using:
Biostar 790gx mobo, amd am3 5200 x2 cpu, 4gb of ram, radeon 5450 512mb video card, 30gb OCZ vertex ssd for OS, 7tb HDD space (All wd green drives, 2x 2tb & 3x 1tb), dvd drive, hauppauge 1800 tv tuner, 350w psu.

All these arnt necessary here is what I would like to do with the system:
Access and share files via local lan and internet. Remote connect to system via local and lan, share media (videos and music) over lan and internet, stream live tv (with xbmc w/ tvheadend?), stream live webcam feed to internet, setup a private proxy server, create an intranet webpage/portal where can access the above features and have info on PC health. Run XBMC as front end for HTPC use.

So what do you think would be the best OS to use for these? I was planning on using light ubuntu which is packaged with the latest XBMCBuntu build. Would a different linux distro be better? Also is all the features that i want above possible or am i thinking of to much? What applications would be the best for these tasks?

I will probably be the only end user of this system, maybe my girlfriend sometimes too but mainly me. Just trying to make my life easier and would love to dig deep and learn some more about linux. Also I am planning on converting all my drives from ntfs to ext4, is that the best move?

Thanks