Is air pump necessary?
 

I have recently set up 55 Gal with 40 gal sump. Should I run an air pump in the display tank? Tank has been running for 2 months water test are good. Any thoughts?

No. Unless you have no other source of agitating the water surface. But you ideally have a skimmer which will do all you need. Especially if it's going to a sump. If not, then make sure the power heads move the water surface. You simply want to off gas the CO2. An airstone would also add tremendously to salt creep.

Thanks Brad. Just want to make sure I don't miss something basic as I start to add more fish etc.