There's no reason you can't use a disc in front and canti or linear in the rear. Since most of your braking force is generated from the front wheel, you probably don't need the additional stopping power in the rear.

Painting costs are all over the map. You can do it yourself pretty cheaply and end up with an OK paint job (check Ken Kifer's website for tips). If you want a long lasting paint/powdercoat job that is really nice try Joe Bell (paint) or Spectrum Powder Works. You can also search the forums for lots of additional info.

http://www.kenkifer.com/
http://www.campyonly.com/joebell.html
http://spectrumpowderworks.com/