Id personally suggest more then just a single core, duel core at minimum.
And also advise choosing a different host from 1&1, as said in shoutbox they require you to phone them to cancel contract with them should you desire to, also goes against their TOS (granted a lot of people use 1&1 to host private servers) but I wouldn't risk it.
As @Arix said in shoutbox try OVH
Specifications Id recommend for starters;
2+ cores at around 2.4GHz
100MBps connection speed
And a minimum of 5GB storage, probably 10GB though Id personally go for 50GB.