I've cleared Skull Castle, but couldn't open a lock in somebody's study. My thief/ninja is level 8 lockpicking, but couldn't make a dent in it.

It says intricate and has 5 stars. What level will I need for that?
Also, I have some books [zenmaster tomes?] that my warlock with artifact level 8 can't ID. Will I have to pay to get them ID'd or should I keep pumping points/training into that skill?
Another also, when should I stop doing sword, kung fu, ect training?
Thanks