Let me suggest that moving from a single-engine airplane to a twin is a large step-up in emergency preparedness training. in addition to retractable gear and constant speed props (which you can learn in a Mooney, for example), you must also learn what to do when one of the engines quits. There will be adverse yaw (due to asymmetric thrust created by just one engine working) and new minimum speeds to learn (such as minimum single engine speed, below which you don't have enough rudder to correct the yaw). Plus identifying which engine quit, and whether it is the one with the most adverse yaw. Other than that, the only big difference is the speeds at which they fly, and the altitudes they can achieve.
You might try googling POH for the model plane you're interested in. POH is short for pilot's operating handbook. If you look, you can find a free pdf for just about any aircraft. Also, google flight review for the plane, and you can read about flying it in magazines such as Flying, AOPA Pilot, etc.
As for the speeds, I make an index card for each of the airplanes that I fly: on it I list clean and dirty stall speeds; best angle/rate of climb; maneuvering speed; gear/flaps speeds; and blue line speed for twins. Plus any quirks.
Cool beans and good luck.