I think the long shaft outboard would be the preferred motor, but some have had success with the short shaft. The motor mount could be a consideration also. Generally speaking, 15 inches for a short shaft and 20 inches for a long shaft. Measured from the base of the engine mount to the top of the cavitation plate. As for the 2.5 Mercury, I'm not sold on Mercury. I just sold a 2006 Mercury 3.5hp four stroke long shaft motor. I had a lot of trouble with this motor and most of it pointed to the carburetor. The orifices are very small and require cleaning often and in most cases require replacement or cleaning with a sonic cleaning device. I'm sure the carburetor for the 2.5 and 3.5 are very similar. Fact is, most of these small displacement motors are made by Tahutsu. I'm a big fan of the black motors, but I think the switch from 2 stroke to 4 stroke may be the cause of these environmental issues which led to problems with the fuel system.. As for the battery powered motors, some look very good, my only concern would be the placement and additional weight of a battery. When I was trying to sort out the problems I had with the Mercury motor, I went on several online forums and found that several other people had the same problems I had with starting, running and idle issues.
So hope this may be some help. By the way, I found a lot of good motors on Craigslist and also eBay. Just finding the right one in your location is not always an easy find. I did buy a 2005 Nissan 3.5 two stroke long shaft motor that only weighs 28 lbs. I understand that some lakes ban two strokes, but also I'm told that it mostly pertains to PWC. Good luck.