The Sunday cat is much more stable than a sunfish. Its easy to launch/rig, doesn't need much for an outboard, and the storage is just right to keep boat toys, lifejackets, etc. on board. Sailingwise, its REALLY easy to tighten-up the sail too much and stall out. I came from sloop sailing and the concept of letting out the sail to go closer to the wind because I'd stalled the sail took some retraining.
The boat moves well enough, but she really prefers a steady wind. Light air can be an exercise in frustration, especially if you are fighting powerboat wakes.
Make sure the rudder is fully down. It makes a big difference if it is not quite all the way down.
If you plan to use the boat as a swimming platform, know that it is a major pain to use the tiny stainless steel ladder and crawl around the gallows to re-board the boat.
As you add weight to the boat, water will shoot up the jam cleat for the dagger board.
Make sure you put a safety chain on your outboard. The poly motor mount on mine cracked, and I never trailered with the outboard on the motor mount.
When raising the sail, the halyards are different. The peak halyard is 2:1, the throat halyard is 1:1. I pull both, then pull the throat halyard, then pull both until the throat halyard is fully hoisted, then I set the peak halyard where I want it.
Human ballast has a great influence on the sailing. Keep it pretty flat if you can.
I expect you are going to greatly enjoy the boat. Its a lot of fun for my family and I. Fair Winds!