Nothing extra needed as a Washington driver for a diesel pusher with air brakes.
Renting from a friend is a personal thing that really depends on your relationship with the friend and if you have a history of using each others stuff. We all have friends we would consider renting to, and friends that are a definite NO.
We all have little boo-boo's inside and outside of our motor homes. I get little ones almost every time we venture out, mostly due to the kids. It's the nature of the beast. It's not like renting a car. And odds are the friends rig isn't as indestructible as a cruise America rv.
But most everything can be fixed and made whole.
Hwy 1 from San Francisco to Legget jct 101 nearing eureka is pretty brutal. Very windy road, narrow, hardly any shoulders. Few turnouts. Not a fun leisurely drive in an RV. A fantastic time, however, in a Porsche. While that stretch of grassland/ coast is beautiful. Nothing like Eureka north to the Columbia river. Can't beat the Oregon coast.
In so. Cal. For Disney. Skip the KOA in Pomona, and opt for Orangeland in Orange. Bring a juicer with you for all the citrus you pick at the Rv park. Only a few miles from Disneyland. (On the same road). When were down there not on a Disneyland trip, we still ride our bikes from the campground to Downtown Disney for dinner/movies/shopping. There's a bike trail right there along the concrete river that goes all the way to Newport beach too. There is a theater across the street too. So the wife and I will sometimes ditch the kids and walk over for a date night.
San Fran....closest park is Candlestick. They really pack them in in the summer. And they know that they are kind of the only show in town. Not the greatest to work with, but its a place to plug in.