Well Mom, your plan has a good basis, but you need to do something tomorrow. I could easily tell you everything you should need to know, but that won't happen tonight or my fingers will go out on over heat and the forum will choke on the file size. You can contact me when you come up for air.....
Are you planning to travel with a laptop and a smartphone? If not, add that to your plan right now. In addition, you will need a copy of Street Atlas with the GPS puck, and a little inverter (150~200 watt) to run the laptop on coach power. You would also do well to get a GPS. It does not need to be fancy, but it does need to work. A smart phone would be good to have also.
As to the coach. You have the size about right, don't go much larger, unless it is a real good deal (like a family/friend offer). If you can stay less than 10 years old, that might be a better choice. I can't help more than that because I have always come on what I wanted advantageously.
First, acquire the aforementioned list as soon as you can. It will take time to learn how to use them all. Put the GPS in your car and use it all the time - even when you know where you are going. You need to learn how it "thinks". Then, load Street Atlas and run the tutorials. It can tell you:
1 - Where to look for fuel.
2 - Where to plan to overnight. Walmart, Cabels, Cracker barrel and highway rest stops.
3 - It can direct you to the stops you want to make
How this works:
Between you and the 12yo (at least - my kids started with computers before that) you can do the navigating with little difficulty. Every days starts with the dash GPS loaded with the day's plan. The laptop is running all the time and someone is watching.
Use the smartphone running "Gas Buddy" to find the good prices along the route. Sometimes you will buy fuel in advance of need. Like when you are at the west end of Indiana, buy before Illinois. Remember to update Street Atlas to the next fuel stop is properly predicted.
You should expect to stop about every four hours for a "Grass Stop". The dog will tell you all about that. Always provision at least three days in advance. Watch water and the black/gray tanks. You will have to learn to dump those. Most Iowa rest areas have a dump. Other than that, except to need to dump every third or forth day. You will have to hammer on the kids that they are not on a city water and sewer. (You don't leave the water running when scrubbing teeth - etc.)
About the route. Don't go north of Lake Erie, it will be a waste of fuel and time. DO NOT try to negotiate NYC... Set a target on the Tappen Zee Bridge. There may be some foolishness there hooking up with I-80 to go west because the RV may not be allowed on either GSP or NJTP and I can't remember which. Other than that.
Things to see on the way:
At Erie is their maritime museum.
Cleveland has the Rock and Roll Hall of Fame
If you have the time to detour up into Michigan. The Henry Ford Museum complex is bound to dazzle the boys. (if you can make that, contact me for the stop.)
Well Mom, this is enough to get you started. If you need me, I am here a lot.
Matt