best thing to do is get you another computer dont have to be top of the line set it up next to the pc you use and just run shoutcase off that one and you have no problems running it cause its right next to your real computer
You have plenty of hosts to choose from,i would recomand you www.ev1servers.net or www.servermatrix.com (aka www.theplanet.com).It doesn`t really matter what configuration you will pick for it,something with 1-2gb ram should do the trick,but be shure you have A LOT of bandwith,500+ listeners means aprox 500*3-4mb / 4 mins.
Where do you need to host? It's probably better to get a server closer to where your target audience is. If in the UK, bandwidth pricing has dropped significantly of late and it's now much more competitive over here.