I have Twin Commander experinece in 500's and 690's, and was a check airman in the TurboCommander. they're decent airplanes; large in size for a light twin, a little heavy, very stable. Dogs in ice. They have a big airplane feel to them. Their single engine behavior is benign. On a powered-back descent, there's no discernable change in feel with loss of one powerplant. I've flown them on fires, on charters, and for the government. They're solid, nice-flying airplanes with a few gotchas.
Make sure your wing spar AD is done; best to get it done one time with the wring root mod. I've done five of them; they're a bear, but it beats having to strip out sealant and go back in repetitively.
Where many aircraft should be configured by the FAF on an approach, the Commander, especially on one engine, should be configured only when the landing is assured, and can be assured on one engine.
Know your systems, especially your hydraulic system. Keep your struts and pistons clean. I've seen several commanders geared-up given failed seals, largely due to failure to keep them clean. I've also seen hydraulic failures and seal failure from using the wrong fluid (skydrol).
The fuselage tank continues to be a source of leakage, with potential for explosive vapors in the baggage area.
On the ice question, you may hear someone say the Commander handles ice well. I can testify to the fact that it really doesn't. I was with the chief pilot of a charter operation once, when he asked a new-hire class how much ice the commander could carry. He went on to say that the Twin Commander can handle as much ice as one can hang on it, and will only lose 15 knots.
I happened to be with him when we picked up ice. We lost 50 knots in less than a minute and couldn't maintain altitude. Damage was done to the airplane from ice coming off the props. The commander is a stable instrument airplane, but avoid ice if you can, regardless of the protection the airplane might have.
Forget the autolean feature. It's not what you think it is. Lean manually. If you love your motors get multipoint monitoring, and lean manually.
In my paranoid mind it becomes a question of: yeah, I know the highest peaks have the most snow, but what if one peak somehow didn't get any snow and is higher than the rest...? We'd probably not see it. It's a terrible mindf**k.
A good reason to fly airways with MEA's, especially in that part of the country. I flew air ambulance up there a lot. The tallest hills in the lower 48 are down in that neck of the woods, near Bishop.
It's always a good idea to carry a roadmap, along with sectionals, WAC's, and low altitude enroutes. Even when flying VFR. Roadmaps give important clues about terrain, including the best paths through terrain when flying.
Congratulations on your safe trip. Enjoy your new ride.