A Minecraft server takes up both RAM and bandwidth. Also, there are a lot of bugs, for example I know of a bug that hard-stops the server when you open a Blu-Ray R/W drive on the tower. You would be better off getting a virtual machine or a dedicated server through a well-established company.
However, if you decide to go ahead with it on your own machine, the suggested RAM to set aside for it is 1GB for every 20 players. If you want to include Bukkit, the suggested RAM starts at 1GB/10 players and goes up the more plugins you add. As for bandwidth, to be honest it will completely depend on your traffic. For about 5 players spending 2-3 hours/day on a Vanilla server, you'll use about 25 GB/month. Bukkit servers will, again, make that amount rise dramatically.
As for killing the server, just type
into the server console, and it's done. You may want to delete the files afterwards as well, and if you have any 3rd-party querying set up (server status websites and widgets) you should unsubscribe from those as well.
Hope this helps, even if it is a little bit late. Maybe someone else will find it useful!