I doubt the wheels will fit directly. The freeride uses basically the suspention from the 85cc juinor bikes but set up differently. The axle size has changed bigger and littler over time for the ktm range as I understand. Simple enough to compare yourself.
How about government incentives since you state you have a plate? I watched one on line video pertaining to Zero and the spare battery had a higher percentage government program than the motorcycle as a whole.
I would not expect more power from a new battery but more capacity yes. It may take a few hours at the ktm shop to get your bike to accept the more modern battery if they have not done it lately. I would try and get a package price for battery and adapting to the bike. Even then it may be problematic for a few charge cycles.
I would ride the bike around a bit first, the way my knees hit the sides seems to irritate me, I do not wear knee pads. The short suspention and declining thrust past 30 mph or so, and the balance of it may or may not lead to deciding it is most suited to having a dog chase you or something of that nature. If it had a way to tie stuff on to the sides or back it would make a much better work horse type of trail maintance bike. No exhaust pipe is great, very narrow.
It has been out for quite a while.