If your transom is in good shape I don't think you need any additional support. My tiller motors have always been clamped (not thru bolted) straight to the transom with no extra backing material, going on 20 years on the same hull. Just get a bolt lock to secure the motor from theft.
Hope...
I also ordered a new aluminum prop for it. The stainless one that came with the motor is a little bent and it vibrates the motor so I will use it as a backup. I debated whether to go stainless or aluminum and I think for my purposes the aluminum works.
Solas Amita 3 10"x11"
The Nissan/Tohatsu 25hp and 30hp models are built on the same block and most parts are the same except the 25 has a restrictive gasket for fuel flow entering the carburetor. So by swapping out a gasket in the carb and adjusting the timing wheel you can get a little more horsepower but it kills...