i've seen videos on Youtube where people have kept tropical fish with the pickerals. Also i researched that they can live in the high 70s.
Just because you seen it done on youtube doesn't mean it is healthy for the fish. They can live in higher temps for a short time. I have found though that after a few weeks at extreme temps (76 degrees +) they become stress and develop fin rot easily.
A redfin will seldom exceed 10 inches( I have never seen one over 11). I have kept redfins and grass pickerel. I have bred grass pickerel. And you can keep a group together in a 75 until they reach about 8 inches. Then I would recommend only two in a 75. I have two in a 75 now that have spawned.