#1 about licensing a driver for a RV, and #2 about what vehicle/trailer/load combinations are treated as commercial in each state, are two different questions.
Driver's license reciprocity usually holds for RVs and other private vehicles, but for vehicle licensing there is a big gap between what each state considers private/noncommercial, and what the DOT mandates as commercial, and some states apply very low weight limits, while oters give private use exemptions for some vehicles well over the 26,000 GVWR the DOT wants to see uniformly licensed.
For state by state details, you may not need a lawyer, but you need to see the law books, and not rely on opinions of those of us who don't know the details.