The short answer - no one knows. It waries on your coding style and type of the game (how much players will click).
Bandwidth: 30-50GB should be enough for a while.
Discspace: nothing, only vistors statistics will eat it up (I used to had one month statistics file of 100MB).
Memory: 64MB if you are using CentOS+LXAdmin+lighthttp, otherwise minimum 256 (but you could get away with 128 if lucky)
CPU: Double Dual Xeon

OK, joking, 1 CPU should be enough for your first 1000 active players (active, not online).
As for recommmendation, check the hosting topic (I saw it somewhere...)