You don't need nutrients for the first couple weeks at least I don't think...
I'll be honest, I know little about growing in rockwool - but search youtube for "I grow chronic" and there should be videos of a green guy telling ya how to grow in rockwool - from what he said ya just soak the cubes then plonk the germinated seed in and wait...
Nutes - Vitalink do some nice ones and that green guy appears to be using general hydrophonics flora series nutes...have a look around!