Lighting Questions

Should be fine. I would imagine the lights have a working range of 10v - 15v. Might be worth checking with the supplier first though. I couldn't see any details about the tolerances on their website.

I've used household lighting in My van, a combination of fixed and adjustable fittings powered from the leisure battery. see http://www.screwfix.com/prods/98827/Lighting-Lamps/Internal-Lighting/Rec... and http://www.screwfix.com/prods/17802/Lighting-Lamps/Internal-Lighting/Kit... for details.
I've also replaced all the bulbs with LED equivalents (from http://www.jmgoods.co.uk/acatalog/Other_LED_Products.html )

These are quite expensive to buy but they last longer,run cooler, and use far less energy than standard bulbs.
So Your batteries will last much longer.
The LED lamps from J&M are rated from 10 to 15 volts so could be left on with the engine running and the van's alternator charging the battery (usually around 14 volts)

Domestic type LED lamps are usually rated at 12 volts only
and need a regulated output transformer (called an LED driver)anything over 12 volt will soon burn these out.

a unlikly place i found was ikea when shopping there with my mrs (world of pain)they have some very reasonably priced 240 small strip lamps if you use a mains hookup also a good selection of low voltage stuff hope that helps