Excuse my ignorance - I've never run DC cable before!

I'm installing some of these...
http://www.tlc-direct.co.uk/Products/QLCD10C.html

Various ways of grouping them are possible, using various transformers
(e.g. one 0-250W, a few 0-50W and 0-100W).

I've done some quick calcs of the required cable size, and it seems
stupidly large.

What size cable do people use in practice? How do people usually group
the lights? Big groups / small groups? Daisy chained cable or star
wired?
Also, what _type_ of cable? What core colours for after transformer?
(On site guide allows almost anything for ELV).

TIA.

David.