So there's no wonder solution then
Decent correction first time around. 95% correction. Pros achieve it. I managed it a few times on the Clio, but that was ridic soft paint.
When buffing off c5 I've read that the left over residue on your microfibre can crystallise, so you need to wash it straight after. Is there anything specific I need to use to stop this?
Not a lot you can do, by memory. Certainly wouldn't be using the buffing towels on paint work again. Probably demote them to plastics or arches, just to be sure.