RE: Motor Size For J3 Cub?
I have the H9 40 (80" wing sapn) version with an older Saito 80 in it. I love that plane and like Mike mentioned; it is a lot easier getting that plane with a two piece wing to the field. You could fly that plane with less motor, but the 80 is a good match.
I would also have to agree with Mike about the covering. Fabric looks more scale like, but the older cubs that I have seen covered in fabric, start to look a little sad when they start getting some age and many flights on them. I still like mine though and when it's in the air it's hard to tell the difference in ultracote and fabric. Just my 2 cents.