are there any plugins similar to mcmmo or possibly an mcmmo port?
Similars plugins yes, clones no.
For example this one https://github.com/NeumimTo/NT-RPG
gives you a lots of more options than mcmmo, but with some extra configuration you should be able to create very similar gameplay just as mcmmo.
Not finished, i have to wait until sponge implements one or two events.
then there is GitHub - AfterKraft/KraftRPG: Implementation of KraftRPG-API for SpongeAPI no idea if it is still in development.