A mid-length barrel with iron sight using Aero Precision M4E1 upper?

The gas port on a mid length barrel is at 9 inches. If you want a gas block with a front site integral to it, I don't think you could do a 9 and a 12 inch hand guard is definitely out. But, if you were to use a low profile gas block that would fit under the rail, you could use any hand guard you like. Mount a front site, via the top pic rail, to the end of the hand guard.
 
In general 9” handguards work with standars fsb and mid gas.

None are 9” exaclty. Usually they are a bit longer, even if not listed in description.