Bukkit is the new replacement for HMod after Hey0 stepped down. Most people will have to switch from Hey0 to Bukkit now, which they would eventually have to do anyway as most the plugin makers have started modifying their plugins to work with it.
Processing power isn't as important and Memoery right now, most dual core processors can run the server, but you will need 1gb+ of free RAM to host the players. Bear in mind that is 1GB after the amount taken up by your operating system not before.
Do players get referral points or something? I keep seeing advertisements for miner wars in every minecraft forum I visit. THe game is an FPS and doesn't look like it has any freebuild aspects at all.