George:

First, thank you.

The outlet area will probably be best somewhere between scale and "Huge." As has been almost said, the outlet free area should be at least as large as the fan's swept area. Any restrictiion causes a real drop in efficiency, and can cause overheating due to reduced air flow.

Down and dirty 100% accurate is the area of the fan circle, and subtract the area of the hub. 75% of the fan diameter is usually close enough.

On the front side, the more intake area, and the smoother the flow, the better. There is a practical limit, of course. A rule of thumb, again - inlet area twice the outlet area.

Enjoy the plane.

Bill.