i dont wanna overload the tank, so in my 12 gallon i put in today 4 tiger barb and 2 peppered cory cat. i read the cats are school fish. so if everyone does well in a while i'll add 2 more barbs and 2 more cats. will the 2 in there now feel lonley?
Tiger barbs probably weren't the best idea for a 12 gallon tank. In the end I would add only 1 more to have a school of five. That seems to be a majic number with many aggressive fish. It should mean they will be aggressive to each other and not the cories.
And then add 1 more cory for a total of three. Then I would stop at that point. More fish will just be pushing the limit of that small of a tank.
And ditto for the pleco, not a great idea. Algae can easily be controlled using an algae scrub pad.