first of all, working on a hybrid is risky business if you have never done it before and the risk for injury is high. you must de activate the system before performing any functions for your own saftey.
the b1s1 code could be open wiring or a bad sensor.
the too lean could be a result of the first code or a vacuum leak. must be re checked after the o2 is working properly. a smoke test will verify a vacuum leak location.
not sure on the 3rd code but will keep looking.
i suggest you let a shop point you in the right direction with a pinpoint real diag, not a code pull. that way you are sure of the failure and you can get a bid for the exact repair.