I would use lights the same or similar to this one
http://www.jcc-lighting.co.uk/product_JC94014
This type of light sheilds the lamp which gets very hot from debris which could be flamable. Also the material inside expands to create a seal in the event of a fire to act as a barrier between floors.
You could go low voltage, but this just adds more components into the system that could fail.
The amount of lights depent on the decor. Dark floors, walls and furniature will require more than the opposite. As an estimate and a starting point I would go with 12.