Fish Stocking As New To This. Also Pump Advice.

I have read on this site that a tank should be at least 6 times longer than the size of the adult fish to be kept in it. now my tank is 23" square by 32" tall so am I still to go by its length or because it is a tall tank do I use a different formula? I have calulated thats a 62 gallon tank (285 litres) so was thinking maybe an external filter ? and does anyone have any idea how much electricity the pumps filters an lights use. I want to get real plants when I set the tank up and understand that two smaller lamps might be better? or is that just for long tanks as opposed to my tall one? I also live in a hard water area.