I would start by reading thru this post -
Anyone interested in 83 Pace Arrow Tear down and Rebuild?. The owner is about to move into year three of a restoration effort.
For now leave the power train alone and focus on the house side of the rig. The drive train is a lot easier to rebuild and has a higher potential for success than the house. If you can't get the house side to work any funds spent on the power train may be difficult to recover unless you find the right person to buy the parts.
Watch the weight of everything used to rebuild the house side. You don't have a lot of tire/wheel/axle/suspension capacity and every pound you add via construction "to make things better and stronger" is that much less you have for cargo.
Keep in mind you'll never get close to recovering any money spent to repair and update the coach. It will be a labor of love to an object that will never love you back. Keep thinks simple and easy to repair or maintain. Simple doesn't fail as much as exotic or complex.
Good luck.