I have six adults, all around 6". Sometimes they swim round together as a small shoal but more often than not they just do their own thing. They do like to just lay dormant as well on a rock or piece of driftwood. So I wouldn't really say they're an active schooling fish.
I have a mix of sae and reticulated silver flying foxes...they are quite similar but I much prefer the foxes for looks...I had a group 3 in one tank, 5 in another, and 2 in another....the three kept pestering each other until there was only 1 left, the 5 are doing great, the two just stay out of each other’s way.
I’d recommend a group of 5-6 for sure and if you want different looks mix them up like mine. Mine are always busy and moving, they usually group at feeding time