In my experience, I need quite a bit of cherries in my tank (17 gallon) for decent algae cleaning. Even with 100+ in my 17 gallon heavily planted tank, you do not see them too much, unless I put food out for them at the front of the tank.I can imagine you being right about only 2-3 being hard to spot in a well planted tank. I could get a few more but I don't want to get them reproducing left and right overrunning my tank with tons of shrimp babies. Maybe 5 or 6 to start with? I don't need them to be the main attraction in my tank.