Great to hear about the fry you already have.
If the tank gets too crowded, the pair will just either lay fewer eggs, or start to cull some of the younger ones on there own. In the wild they live in very densly populations, so I would imagine that they will allow quite a bit before they will worry or act upon it.
A word of advice however. If you have any intention on raising many of the fry, it would be wise to do so in a seperate tank. I have found that the young will become very teritorial when a little older. The eldest of my fry are only 5 months old and are little terrors. I have 4 in with the parents, and they are not so bad with picking on each other as the others are who are in there own tank. I have 9 others in a 20L, and they are already becomeing amazingly teritorial, and begining to be brutal to some of the weaker siblings.
As I said, the ones still with the parents are not near as bad as the ones on there own, so perhaps the parents keep those in line and therefore there aggresion is not as bad.