Increasing the numbers of the silver dollars would be a good start. They're shoaling species and they really like more than four. Even just six would be good. Pictus cats are shoalers too, so increasing those numbers would be good and I don't see a problem with them being tank mates. Other large tetras would be a good idea. Buenos aires come to mind, giant danios, larger black skirt tetras (don't get the small ones, find someone who has big ones), corydoras could be good as well for bottom dwellers. Lots of options.