If you rent from a reputable company, like Cruise America, they will have a helpline you can call to answer questions that crop up underway.
Dumping the sewage: If you choose parks, this will usually be available right at your site.
Generator: It depends on your set up and where you choose to park. If you are at parks with facilities, you can plug in the vehicle, rather than running the generator. Otherwise, you may need the generator to run the AC in extreme conditions. If you wanted to stay someplace for a long time and run the TV and other toys, you would use the generator to recharge the batteries, as well. Heat may be on the generator or it may be propane heat.
Inclusions: You need to decide what works for you. We rented near home, and so did not get any of their packages, we just brought our own bedding and kitchenware. If you are flying to Pheonix to rent an RV, you will probably want those packages. With Cruise America, we didn't come across any surprise fees. You just need to be aware of your mileage.
Parking: I always park an RV on the far side of the parking lot from what I am going to, as it doesn't fit in a normal space. When we did a Grand Canyon trip, the Grand Canyon park was our only park. Everywhere else, we just went found recommended parking spots. We parked on one side of Sonoma on the way there, and the completely opposite direction on the way back. We parked on BLM land in the middle of nowhere one night and accidentally parked within eyesight of a border patrol station another night. They use very bright lights, we weren't able to stargaze at all.
I highly recommend the Grand Canyon RV park, as it allows you to take the shuttle bus to visit other areas of the park. This way you can have two or three days (or more if you are hiking a lot) at the park, without dealing with traffic at all.
