The electrics circuit is simplicity itself. Its a good idea to maintain a consistent colour scheme and one way plug arrangement to maintain polarity. The charger will be fussy about polarity but most can be rectified by a simple switch if you have messed up your wiring. If you progress to an HID light head then polarity will be more crucial.
I used what are commonly known as 'Tamiya connectors' by radio controlled enthusiasts. They can be bought assembled with leads or as separate terminals/shrouds etc that you solder up and assemble your self. The leads that Maplin supply are six inches this wasn't enough to connect to my negative terminal on my battery pack at the bottom of the pack and reach the top (about 9" away). I compromised and used a connector block to join a wire already soldered to the - terminal to give me the length I required. If I was doing it again I would make up the leads myself.
I used insulating tape to hold batteries in the correct orientation while soldering. It is also a good idea to use little heat sink tweezers to stop the batteries getting damaged by the heat of the iron. As can be seen in the diagram the wiring effectively makes a chain going form negative to positive through all the batteries. There's nothing much to it just make sure you know what your connecting.
This arrangement allows the battery pack to be unplugged from the umbilical/switch assembly for charging. The Maha charger conveniently has a socket that allows the tamiya plug from the battery pack to be plugged straight in.
The bottom picture shows the canister lid the cable coming from the lighthead enters the canister via a cord gland. The positive wire goes to the switch, hopefully the diagram is self explanatory.
I haven't given any info on lightheads, as I haven't finalised what I will use yet. Basically, in terms of the wiring it doesn't matter you will have a lamp holder at the end of the umbilical all switching is done at the canister.