RE: DLE20 discontinued?
The size of the battery is like anything else. You need to have enough battery for the amount of time you want to fly. Ignition systems are pretty simple and you can get away with a simple Ni-cad or Ni-mh battery. but the Li-Fe will work as well.
standard servos will work fine. But you don't necessarily need a choke servo. If you have access you can just manually choke the engine. Or put an extention on teh choke so you can reach it inside of a cowl or closed in area.
Ken