well the ornate will eventually need a larger tank as they can reach a bit under 2 feet (although around 18-20" is a little more realistic) but if you get that problem ironed out then for the smaller species that stay around and under 1 foot, you could get around 4.
Delhezi, Senegal, Palmas sp's (palmas, polli, buettikoferi), retropinnis, mokelembembe, and its stretching it greatly, but perhaps a weeksii for quite a while but it would probably need a larger home eventually.
i had four in my 55g, 3 sens and a retro, and they looked a bit cramped. They were all between 5-7" so at a foot a piece fully grown i think 48" tank may be too small.