Slight correction: The later variants are turbocharged, providing greater-than-sea levl manifold pressure ie boost. Turbonormalising is a form of turbocharging that only maintains SL pressure at altitude.
Learn the immediate action engine failure drills until you start mumbling them in your sleep. You don't have to rush them when they're used - better a slightly slower pace to make sure you don't pull the wrong knob - but you *do* have to know them.
The Seneca is a Part 23 light multi <6000lb MTOW and Vs<61 kts so +ve climb performance on one engine was not required. Only that what ever performance it has "...be determined". That determination could be downhill. Further, like all other light twins, whatever best climb (or slowest descent) performance it has when asymmetric is only under a very limited set of conditions to minimise drag. Fail to meet those specs. and you can kiss any expectation of meeting book performance out the window. *Don't* get into the mindset that the 2nd engine will always enable you to continue flying!
A failed engine also adds a higher probability of losing control due to the asymmetric thrust. Conditions that are beneficial to better single engine performance act opposite to conditions that provide better single engine control and vica versa. Don't confuse asymmetric *control* with asymmetric *performance*. Further to that, some instructors have been known to teach that best single engine performance will be at 5 deg angle of bank (because Minimum Conrol Speed is determined with up to 5 deg bank). This is not the case. 5 deg bank is solely concerned with *control*. Best asymmetric performance will typically be at 2-3 deg bank.
Remember *control* is more important than *performance*. You can survive a crash that hits the ground under control Chances are you won't survive an out of control cartwheel into the ground.
The Seneca is a simple aircraft. Seneca 1 particularly. Like others have said, if you're flown an Arrows or a Lance you'll feel at home fairly quickly.
Some bits & pieces:
* Each wheel hanging out is worth about an inch of manifold pressure to maintain a descent profile. When the wheels go out add about 3" MP to maintain the current profile.
* Always check the nose locker door is locked before getting in the aircraft no matter how sure you are that the door was closed. It's tempting to close the rear door after loading pax/boxes & walk the shorter path around the tail so you can enter. Don't. Take the the longer way around the wings so you can check the nose locker door. If it's not closed it will fly open just as you rotate and can separate from the airframe. It's embarassing & a poor showing of one's usual care & attention. Trust me on this one...
Might think of more later.