Info for ram usage:
1 player eath up to about 80-120 gig of ram
This number is afected by the amount of plugins you have
On my 4 gig server i could technicaly run 64 slots, but had to cut it in half due to 35 plugins. The slot number is not so important. lets say you have 30 slots, and average mc player plays 2 hours per day, so at most you could have a trafic of player reaching the number of 360 players per day in the optimum case. in real life good 30 slot servers have around 30 regular players and 60 iregular(a lot of players play on a lot of servers).
I curently run a 16 gig quad core linux dedicated server, not over a game host. Got it from a server host, its chaper that way but much more work involved.
Dedicated IP mean its only your IP, you do not share it with other people, but you can still run 10 minecraft servers on that server, all you would have to do is in the server.properties file change the port number from 0-64000. what ever suits you best.
hope i was of help