Hi
@jimer - Welcome to the forum. I split up your post into 2 parts and created a new thread for each and placed them in more relevant sub-forums with notifications back to you.
I've had a couple of coaches with the Onan 5500 in them and they're real nice. In my case, they've always been factory installed. While Alliance uses other brands of built-in generators these days, if you are ordering a coach, I'd have the factory install it during the build.
If you're buying a coach off-the-lot and overall pricing is a concern, I suggest getting an 'installed' quote from your coach dealer and perhaps some other companies (RV, service center etc.).