Don't know the laws in other states, but usually, the mfg gcwr is just a suggestion. If stopped, they look to see that no individual axle or tire is overloaded, and that's it.
Regarding needing a CDL....you don't if it's for personal use. The C in CDL is for commercial. A private individual towing a tractor for personal uses does NOT need a CDL. You might need a different class of non-commercial license, but CDL is not even a consideration unless you are hauling for commerce/hire
Depends on the state. Some states have non commercial class A and B licenses others require you to get a CDL over 26k regardless of purpose. Here is a good reference sheet for RV's. In some states RV's might get special exemptions that don't apply to Joe blow hauling around his personal backhoe for personal reasons.
RV Driver's License Requirements