You made the mistake of not having a 10 year old motor home properly inspected. This is not a Coachmen issue.
I'm sure you posted on this site expecting support and compassion. It's not going to happen. We might feel sorry for the situation you're in, but blaming the dealer or Coachmen for issues on a 10 year old unit and expecting help, is unrealistic. The vast majority of units that old will have issues, it's just a question of how serious they are.
As others have said, you should be putting the blame on the person you brought with you, to check out the unit.
You were told numerous times that it was being sold AS-IS,which is not unusual, yet now you're expecting help with repairs?
You mentioned that you used the cab over for storage. I'm curious as to how much weight you were storing up there.
Of all the issues you've listed, many of which are age related, normal wear and tear items, the rotted out cab over seems to be the most expensive to fix. Assuming it's as bad as you say, it should have been caught, when your friend looked at it. That would have been more than enough reason to walk,(no run) away.
In early June I bought a MH that needed a complete cab over renovation. I bought for less than 25% of what it would have sold for, if it didn't need a complete cab over rebuild.