suggestions:
dont limit per ip, limit per pc. you are gonna exclude alot of players, who are playing from the same network (internet cafes etc.).
at least make it 4 :D iam gonna join with 3 mates and we play at a lan.
furthermore add a lvl cap. without lvl cap you can abuse that system pretty easy. once high lvl, everyone will raise his own buffer / healer / crafter / spoiler. clans will use this, to exp people to lvl 40 for the rep points.