You can rent a Class B motorhome from outfits in the San Francisco area and Class C from other locations and try one for a week. You will learn what is important and what might be a problem. The Roadtrek are great for a single individual. The Phoenix Class B+ provide a lot more space (double slide-outs) but are going to use more fuel.
I see many individuals and couples traveling around with a medium sized SUV towing a small travel trailer like the Burro and Scamp ones. These are short enough to fit in any campsite (even the ones for tent use) with the tow vehicle and fast to unhitch so you can use the SUV to explore. Something along the lines of a Toyota 4Runner or Honda CRV or Ford Explorer are more than enough to tow these trailers anywhere.
In many areas no motorhome, even a Class B, is going to have a place where it can be parked in a scenic spot. Many pull-outs for example in Yellowstone or along the coast highway in California or scenic areas in New England where a car will fit but not even the smallest motorhome or a tow vehicle with a small trailer. Better to park the trailer and explore these areas with the tow vehicle and this is where a smallish SUV is perfect.