I wouldn't hesitate to go with the Saito 72. In fact, for a 60 size plane, I'd go as high as a Saito 100 (although that might be a waste of a good Saito 100 - but a 90ish 4-stroke would be fine)

As far as flaps go, while the PT 60 certainly doesn't NEED them, I've yet to find a plane that isn't more enjoyable with flaps, so I say go 4 it!

It's easy to do too, just use the aileron torque rods to control the flaps, and either run a flex rod out to the ailerons from a single servo mounted in the center of the wing, or mount a servo in each wing.