Without knowing some specifics, (such as weight etc) it is hard to guess for sure. With the 66" Wing span the 91 should fly it OK. It certainly won't be "too much" engine (I don't know if that's possible anyway) It won't be overpowered but as a practice plane to get started it ought to do the basic sequences just fine. As rl56 mentioned a larger engine would be better.

For the prop a 14 x 6 Zinger or APC is a good starting point.

If I was buying a new engine for that size of pattern plane today, I would look at either a YS 110 or Saito 1.25 (With the YS being my preference in such a model).

The trick to enjoying pattern is to just start flying it, preferably with another interested party calling for you and assisting. The feeling when you look back after a gallon or 2 of fuel and realise that you are starting to fly with more accuracyis great - It sure helps when sport flying too. We've all started at the beginning of this sport and we all aspire to be better, I'm sure. I try to practice at least some of my pattern routines to some degree with every flight that I do, regardless of the plane that I am flying.