Apologies if some of this has been done to death in FAQ'd and elsewhere. Struggling to link the various key info from the mire

Right - we have a 2wd drive, diesel, auto bongo, single battery, AFT, manual blinds, non climate control
Its a part time camper and has the original electrics.
I want to put a leisure battery to isolate the lights, stereo, 12v sockets (and have a couple of extra feeds if required in future for things like a chiller), with the appropriate split relay - also want to make sure the starter battery is isolated so you dont have to worry about flattening the battery.
The (currently not in stock) EBay Willinton kit looks spot on - i've emailed the seller asking if there anymore in the pipeline.
http://www.ebay.co.uk/itm/MAZDA-BONGO-1 ... 2109wt_980
I assume i'll also need a way of mounting the leisure battery - under the bonnet is the most obvious - so i presumably need a tray like this:
http://www.ebay.co.uk/itm/MAZDA-BONGO-F ... 337f22aa4a
Then there is the battery itself - read on here that something like this is pretty good:
http://www.ebay.co.uk/itm/12V-110AH-Pla ... 3cc9be1c34
ALSO

I want to get a towbar fitted for (primarily) mounting a tilting bike rack. This will need electrics for lights/numberplate lights etc. Something like this, and what is 12n/12s/7n/7s
http://www.ebay.co.uk/itm/Towbar-Mazda- ... 20baf9f7a8
Basically - tad confused by the different options

Cheers!
Tim