Let's see, a less than one year old boat by a well respected manufacturer, ditto for the motor, means in my opinon. that you have nothing to worry about in terms of; is it mechanically sound, will it give me years of service, is it a good unit?
As to a 40 horse being too much power for a 16? IMHO I think that it is just about right. Two adults = 300 - 500 lbs of weight. Add gear and motor weight + 350 lbs for a total of 650 - 850 lbs the motor has to push. A car with twice the weight has a motor with 3x the hp and is underpowered in some peoples opinion, and it is pushing on asphalt not water.
The price - compare it to the same rig brand new, and you may be surprised.
It boils down to whether or not you feel that this is the right boat for you.
Buyers remorse is always there, however one must remember that at the time it was the best deal that you could find.
If you go ahead with the purchase - enjoy. If not, the hunt continues.