You're asking for a whole country's worth of ideas which is difficult to put in a short post. However, you seem to be zeroing on big cities. That's fine if those are the kinds of places you enjoy. However, with an RV it's so nice to go to national parks, state parks and stay in beautiful quiet surroundings perhaps with a lake or stream nearby. You can always drive into the big cities but do consider staying out of the cities. We use public parks all the time.
As for your wife's concerns - there shouldn't be any. You'll love it once you get going. Costs: other than fuel (estimate how many miles you intend to go x mpg) and campsites (cheaper than motels), your day-to-day living should be about the same as when you're at home. We go to restaurants occasionally, not every day. Buy groceries like you would for home and cook the same way as you always do. Bring your crockpot and start the meal in the morning and go siteseeing.Bring the BBQ and grill a quick meal.
Since you seem to be leaving after August you'll hit the 'snowbird' season for all winter. That will be good for you because you'll find a lot of adults in the park with like objectives - having fun. If you're that type of person, strike up a conversation with some and get their interests. If you find something similar, suggest perhaps going on a hike together or visiting a certain place together or going out to eat. Many folks do this and we have acquired long-term friendships which started out this way. 'Snowbirders' do this kind of thing. :)
It might help, once you have a route narrowed down, to do some individual posts on this forum on specific areas to get more ideas - not the whole country.
To give you a few starters, you mentioned Phoenix. The whole area has some wonderful regional parks to stay at, such as Usuary, McDowell Mountain, Cave Creek, Lake Pleasant. Google 'Phoenix Regional Parks'. They are gorgeous complete with nice easy hiking trails and all are very close to tour the big city. They're much better than the huge RV parks of row after row of sites you'll find in Phoenix. Lost Dutchman State Park on the far eastern side At Apache Jct, AZ is terrific, too. The city is huge so pick a park on the western side and one on the eastern side to explore different areas.
Tucson is another nice 'little' city compared to Phoenix. Catalina State Park is a winner as is Gilbert Ray Campground in Tucson Mtn. Park! Continuing on I-10 eastward, go to Kartchner Caverns State Park near Benson, AZ and tour the awesome caverns. I won't get into state by state here but Big Bend Nat'l Park in Texas would have the perfect time of November for you to visit with the bright yellow cottonwood leaves against the brilliant blue sky for you to admire.Stay at Rio Grande Village campground - either dry camping (our favorite) or full-hookups. Passing through Alabama, get off the interstate and go down to Gulf Shores State Park in Gulf Shores. It has large campsites, close to the beach and town with lots to do in the area. It's unique in that 'snowbirders' can stay the whole winter if they'd like. Usually state parks have a 2-week limit. We spent a few seasons there and really enjoyed it.
One last thing, don't stay on the interstates. Get off and continue your way along the secondary roads. You'll find more scenic views and less traffic by doing so. You've got lots of time now so don't hurry. Have a great time planning - that's half the fun of the trip! Happy retirement!!!