For starters,,,,,,, exhale.
Most 2020 large class C rv's have an onboard generator, that will operate off the onboard fuel tank. Check with the renter, you should be fine there.
Verify the length of the unit. Most parks will help you select campsites based on length and type of hookups you need.
Water and 30 amp power are commonly what is needed, but double check, again with the renter if the unit is a 50 amp service unit.
(hint, if it has 2 air conditioners, its a 50)
Plan your trip with travel days around a 300 mile day, if you are not used to driving and setting up that size and type of unit, you will appreciate NOT pushing farther/harder within a day or two.
Dont get upset if you dont hit every National park in a single 4 week cross country trip. This is supposed to be a vacation, not a marathon, take your time to relish the freedom.