My bristlenose pair just bred again in my 50g community tank. You could set up a breeder tank, a 20g would be good with lots of caves / hiding places, but if they have a cave in the community tank they will probably breed in there anyway. Water parameters are nothing special, just good water quality.
They should breed at around 3 inches, the male will have a full head of bristles and the female will a few 'stubs' or no bristles at all. A pair is fine for breeding. Sometimes they need to be triggered into breeding but from my experience and what I've read most don't need a trigger.
Give the adult pair a varied diet and keep them well fed. When mine are ready to breed they spend a lot of time together, the male will do a crazy wiggly dance for the female near the cave, the female will go into the cave and lay the eggs then the male will go into the cave and look after the eggs. The male will look after the newly hatched fry until they're around a 1/2 inch long.
And I can tell you once they start breeding they won't want to stop LOL .