Welcome, Jeannie!
For the fridge - Propped open between uses is good. Just be sure it's OFF. What Bumpy said above is correct. Underway, the fridge passes "through level" a lot of the time, but stopped, should be level or close to it. Some say "If you're comfortable, the fridge will be comfortable too," but I've seen too many cockeyed rigs on campsites to endorse that message. I consider the FRIDGE the VIP Customer when leveling. Get your coach level someplace. Then check level several places. The Fridge may not be mounted true to the rest of the coach. Ours is, but the Stove isn't. Hard to fry the perfect Sunny Side Up Egg.
Once you find the Sweet Spot for leveling, you need check only there. Do this in the HOUSE, not the Cockpit. You'll be surprised how much the chassis twists, making the cockpit level when the house isn't. Side to side I mean...
EDIT: Forgot the V10 part. MPG is probably best right where it drops into Overdrive, around 45. While 55-60 is good, I'll say you may want to run a little faster if the terrain is hilly. Not mountains, just hills. Reason: With the engine spooled up to a little higher RPM it may not downshift from OD to Third as much. I used to try to hold a steady 58. Then I tried steady 62. Still a fair amount of downshifting. The cruise on these is way too touchy. Of late, I find I'm happier driving without cruise and trying to stay between 60 and 65, trying to work with the hills. Or, in FL, the OverPasses!