Aluminum piston heads just add weight to your piston/piston head... and offer no strength benefit over a duracon or polycarb piston head.
When using a 150 in a version 2 gearbox, it would be wise to use something a little lighter like duracon instead of the metal piston heads... takes the energy contained in the piston down a little bit and reduces gearbox fatigue slightly.
If you're getting a g&p m160, you shouldn't need to use hi torque gears. They will only reduce your trigger response. I pull an m140 level spring, and can do so on an 8.4 volt 1100 mah stick battery with almost no trigger lag using standard ratio gears and the m160 motor. It's super efficient. ridiculously high torque motor = don't need hi torque gears.
As far as wiresets go, they're all about the same, but for the record, I prefer king arms wiresets... easier to cut/strip the motor connectors for installing the m160 (doesn't use standard motor connectors). Plus, the red plastic bits are just fancy looking. lol.
Batteries:
http://cheapbatterypacks.com/index.asp? ... sid=411121They're always out of stock, but good batteries.
Ebairsoft and ehobbyasia both have them sometimes as well. I'm sure there are other people that can help you out more with those... I use a full stock and gigantic lipos.
You shouldn't need one, but they're nice.
Also, just as a thought, you will want solid bushings. Sure bearings MIGHT work, and they might never break... but if they do, your gears will pay the price. It's not an appreciable difference in a semi-auto only gun to go to solid bushings instead of bearings.
As far as buckings go... unless you have a phobia of opening your gun far enough to swap the bucking every 25000 rounds, you won't need a hard type over something like a G&G Green.