Its good to have you, make yourself at home.
If you are putting the hot air into the attic, is it well ventilated? Is there at least 1 square inch of ventilation for each square foot of space? My opinion is that the best attic ventilation draws air from the soffits and expels it at the roof ridge. If those conditions do not exist in your attic, I would recommend that you vent to the outside air.
Most split level houses have 4 or more rooms on the upper floor and 100cfm per room is most satisfactory. So, the 380cfm model is the best for your situation.
The optimum placement would be as near the center as possible. If there is a bathroom on that level with a vent fan, the door should be kept closed allowing the bath to vent independently and having the windows open about an inch would assist in the ventilation.
In my house there is a 36" 'whole house vent fan' in the central hallway which can make the curtains stand out when the windows are opened. You feel like it will take the rug off your head when you pass under it.
Please let us know how it works out for you.