In tank like that i would go for one male and maybe 2 females. Too many males would end up in fights and not enough 'action'. Too many females would not be good for the male.
It takes about 3-4 weeks for a female to be in condition and 2-3 weeks for the fry to leave to cave. So if you had more than 2 females the male will always be spawning and it may be a good thing in the short run but not in the long run.
Having more than 2 females would create a dominant female who will always be after food and the male, which is another down point for having more than 2 females.
Personally i would have a bit of gravel 1-2cm, a small water flow like you said bit of bog wood & rocks and good varied food.
Even if you don't get everything perfectly they would still breed, Just by being on good food and good water.