A few questions regarding setting up a pool

I'm attempting to setup a small pool for me and a few friends and I have a few questions regarding the process.

At the moment, i'm running Bitcoin-qt (with the flags -server and -daemon) on a small VPS hosted by Amazon Web Services that can be upscaled or downscaled when I need it to be - what kind of specs am I going to need when people are mining on the pool?

What is going to use more resources, bitcoin-qt or pushpool? (They are running on different servers at the moment)

I attempted to connect to Bitcoin-qt from my PC with the RPC Username and Password - but i'm getting the error "No JSON object could be decoded" from GUIMiner and "Error: Cannot connect to server" from Phoenix. When I run "getwork" on bitcoin-qt RPC Console, it gets the work just fine so I don't understand why the work isn't getting from Bitcoin-Qt to my machine. Windows Firewall is off, the RPC username and password are both correct and both port 8332 and 8333 are open on Amazon's firewall - what could be the problem?

If anybody could answer these questions for me, or direct me to the correct section to put them in, I would be most greatful.

Regards,
Dorkslayz.