I don't have the answer to #1 but I'll give you some input on question #2.
Wheels and tires are what are considered "unsprung weight". In other words, the springs don't hold up that portion of the chassis. Whenever you hit a bump or dip, the suspension needs to raise or lower the axle so that the coach doesn't ride like a lumber wagon and also so that the tires remain in contact with the road to give you safe traction rather than hopping off the road. That's the entire purpose of a suspension system. When you encounter a bump in the road the axle will start to move up and compress the springs and shock absorber. Once the axle starts to move up it's the duty of the shock absorber to return it to the road as soon as possible rather than allow the springs to let the coach bounce back and forth or porpoise down the road. The shock needs to control the unsprung weight. The lighter you can make the axle/wheel/tire assembly, the faster the shiock absorber can do it's job. Therefore, having less unsprung weight is an advantage. Aluminum rims help in this regard because they are lighter than steel rims.
Another benefit to aluminum rims is that the run truer than steel rims. This helps to keep your tire assembly balanced. Aluminum won't bend like steel so they'll stay true unless you hit something serious, in which case they'll crack and totally fail.
Also, last but not least, there's the "looks" factor. Aluminum rims look cool.
You also don't have to deal with the stainless steel trim rings used on steel rims, which can give you headaches (and cut fingers) when dealing with valve stems and extension.