From what I've read probably the most popular choice is the b40-8l on 8 nicads or 3sXp lipoly. If you want to run 10 nicads you may consider a 9l or 7 nicads a 7l but the 8l seems to be the most popular.
For the controller, bec means you don't have to have a receiver battery. In a bec controller the esc will give juice from the flight pack to power the radio gear. Opto means that the esc will not provide power to the radio gear and that the power to the motor and power for the radio gear are completely separated inside the esc.
Opto is less chance of interference and much more importantly most bec will not work with 10 nicads or more and even on only 8 nicads most bec will not provide enough current to operate the 4 servos and a gyro that a helicopter need. Usually with a heli you are stuck with and safer to go with an opto esc and a ubec for powering the radio. The hacker 40-3p and 48-3p are popular controllers. A castle creations phoenix 45 would work for this bird as well and be significantly cheaper and easier to get repaired.
I would personally recommend a b40-8l on 3s3p TP 2000 lipoly batteries with a castle creations phoenix 45 and a koolflightsystems UBEC.