IME Tropicals (cichlids, cats, bichir, knifefish) mix fine with natives (variety of sunfish and a bullhead cat).
On the issue of quarantine, this is a must unless you are willing to gamble on you tank getting nasty's in it. I actually did not quarintine my big bluegill and am extremely happy that nothing bad happen. But on my next catch, 2 bluegill and a pumkinseed, I quarantined them for a month. Again no nasty's present but I was able to adjust them to tank life easier in a smaller tank, letting them know that pellets are food, so when they joined the others they knew they had to compete for food.
I've never kept a perch or bass, although I plan on keeping a bass, but I hear perch can be tricky to make the change to prepared food.