In regards to reef current, 10 times the tank capacity turn over per hour is a good rule of thumb. That also depends on the species. A good idea is to point your powerheads towards the surface which is where the majority of O2 exchange will occure. The more suface agitation that you can get, the better off you will be.
On a side note: Running air through your powerhead does very little except cutting down the flow of the powerhead and creating a mess through salt creep.