For Plug and Play, assuming Champion level, that is what you need -- kit, LED, momentary swtich. The Kit includes the Sabercore board attached to a battery/holder wrapped in heatshrink, all the wires with quick connects, and the recharge port ready to be connected.
The Hero kit includes everything, and the Warrior kit is just the battery holder with wires... you'd need to add latching switch, led, battery, and charger to that one.
The recharge port is kind of self-explanatory, you plug the charger into there instead of taking out the battery. It also, in conjunction with a kill key, acts as the "off switch" for sabers with soundboards. Someone more versed with the electronics could probably explain it in more depth that I can.
A 12" hilt is about the average I would say. It wouldn't want to go much shorter for a two-handed grip.