Of course the more the merrier, but I find it difficult to get more than 50 rep per attack. I'm assuming rep gain is related to fair fight (maxes out at 3x, which is the case for my targets) and the level of the target, but even with the search tool it has been difficult to find higher targets. Is 50 an acceptable amount, or am I doing very poorly here? 

For your level that is pretty good I reckon. My average per attack is 47 :-)

100 rep per target is good enough