Sounds like an awesome trip plan, Mik.
I'm not sure if you are aware that the roads are smaller on the eastern side of the US than out west, and that driving a big rig there can be a bit of a white knuckle ride.
You might be happiest, if you are focusing on the eastern states, to get a class C or smaller trailer. Or, keep with your big fiver plan but spend some time in Utah, Idaho, Colorado and western Wyoming, which have some of the most beautiful landscapes in this country, and save the eastern states for a road trip by car or smaller RV...