one thing i found out after buying a few spokes, was that it is cheaper to buy one of these IF you plan on doing more than one or two builds...
http://www.ebay.com.au/itm/Hozan-C-...394218?hash=item2a6395e4aa:g:2zcAAOSwHxVW7Ojl
it does need a different head for the 12 guage spokes... me? i would just use whatever i find, if its 14...its 14. drilling wont hurt the hub though. usually.
spokes arent exactly cheap... especially the stainless ones. well, over here from "the local bike shop"... might as well be made from platinum with the price they ask!
use the length calculators found online, its pretty straightforward, especially with single sprocket hubs. gets tricky when you use a 10 sprocket cassette with the massive offset on one side. or cross four/five, etc.
there isnt much need to go past cross 3 anyways. as long as you dont go radial...
once youve done it a few times, lacing a wheel is pretty easy. even then, its once you start the last row that you realise you have stuffed up and have to undo most of them again...
avoid deep section rims, they can be a challenge(read, nearly impossible) to get the nipples in.