If you are only adding this one more species of fish, then I would put as many as you feel your tank will handle, with corys the more the merrier. I went with emerald cats (very similar) and started with 6 in mind, ended up with 9 (at my max now) and I have already seen them patrolling the bottom in one big group quite often, after only two days in the tank.
I haven't done the math, but it looks like Byron has, 9 or 10 would be ideal.
A quick thought regarding hitting the "minimum" recommended number of shoaling fish. Aim for a couple more than minimum so that if you end up with some loss you don't have too few... not that we plan for losses but it happens.
Jeff.
