I was stoked to see the 1997 International Amtran recommended, because I've got a 1999 International Amtran...very different buses in many ways, exactly the same in others. That said:
The DT466 is not a fast engine. Everyone I've talked to who has one agrees with my experience: it's a dog at acceleration. It takes me at least a quarter-mile to get up to 25 mph, and if there are hills along the way you'll be lucky to keep it at 35. For highway driving, they're great once you get them up to 65, and will happily motor along at 70 mph for days as long as you don't come to a mountain pass (or even a large hill).
I would have loved to get 4WD, but didn't know such a thing existed when I bought Velda - instead, I opted for buying a bus from a snowy, mountainous region which came equipped with an electromagnetic brake retarder and automatic chains. Unfortunately, since I bought it sight-unseen, I took the seller's word that these features worked. And they don't. (I recommend NOT buying a bus from the Adams 12 5-Star School District, just north of Denver, CO) The moral of that story is to verify that any features you want actually exist on the vehicle, and that they work, before you hand over the money.
As for navigating twisty-turny roads along the Pacific coast, I'd recommend that you look for something no longer than 35'. Velda is 39.5' long, and she's not particularly agile when it comes to driving in confined spaces. Heaven forbid you have to do a three-point turn with a vehicle that big in just about any forest setting (it's nerve-wracking).
All of your criteria regarding electrical power and usage are moot when you're looking at what type of bus to buy, as you're going to be adding those features (with the obvious exception of storage space for your batteries and other equipment). I would recommend NOT going with an electric on-demand water heater, as it is going to use more power than you can probably store or generate with solar, unless you're looking to invest some serious money in your electrical system (Batterie$$$$).
Good luck!