The Fluval (Aquaclear) 70's are good filters. I personally run a 70 and 110 on my 55, but your stock load is relatively light. I think you'd be okay.
As far as the fish only being active when you walk away, it's my experience that it is an instinctual thing when you only have 1 or 2 cichlids in a tank by themselves. They're staying out of sight so they are safe. I've had good luck by adding some smaller, active fish (tetras, danios, barbs) that are out and about. It will make the cichlids more comfortable.