Do not build your own packs, It is very easy to damage the cells by overheating them, leave this to the experts. For a standard 60" airplane running 4 or 5 standard servos, 600-700 mil nicad pack will work fine if your not doing a huge number of flights. double that if your going with digital servos. You may want to add a little more NIMH cells. Charge your batteries over night at 1/10 th thier capacity, 100 miliamps for a 1000 miliamp pack. The Pack that came with your radio will probably work fine and thier is no reason to run 6 volts unless your are running a high performance application such as 3D etc. Sounds to me like you have yourself completely confused about batteries. Don't waste a bunch of money untill you understand whats going on.