I'd avoid 2nd hand hydraulic disc brakes if you are not familiar with them.
Either cable disc brakes - Avid BB5 are recommended or hydraulic disc brakes - Shimano deore are often available cheap from online shops.
http://www.chainreactioncycles.com/Mode ... elID=87317
- buy two of these & a different adaptor for the rear & you will have some mighty fine brakes for under £40 - rotors included!
Your forks are post mount so make sure you don't buy any IS mounted brakes otherwise you will wish you had stuck with vees!
Hub wise if you are happy with deore, then these in either 6 bolt or centrelock mounting will be okay, personally I find that going the next step up to either LX or SLX hubs is worth it due to the better seals.
Subject to your riding & weight I have found it worthwhile to go 180mm disc up front & 160mm disc at rear.
Look out for some good wheel & disc brake deals on Merlins website