I've never had Apistos, but my flag fish have never chased any of the others. In fact, when I first introduced them into the tank, they took one look at the tetras and "ran" to hide (my tetras are pretty big and VERY active). Now everyone gets along very well.
As far as getting at least 2 to keep each other company, that's what I did. My LFS said I should probably get 3 or 4 so they feel more comfortable together, but I decided on 2 since I didn't want to overcrowd my tank.