First step will be to decide on whether you want a 360 mm or 240 mm or 280 mm AIO. Don't buy a 120 mm AIO, better to just buy an air cooler.
360 mm will have 3 fans of 120 mm each. 240 mm will be 2 of those fans. Usually all our case fans are 120 mm.
280 mm will have 2 fans of 140 mm each. They...