So long as the total Gross Combination Weight Rating of the vehicle is 26,000 lbs. or less, and the weight actually remains under 26,000 lbs., then no, you don't. You also don't need a CDL if it's a vehicle exempt from FMCSA regulation, such as a recreational vehicle.
That depends. CDL requirements depend on the weight rating of the vehicle, not the weight it actually is. If you need a CDL for it when it's loaded, then you need a CDL for it when it's empty. If it's a single vehicle or a combination rated at more than 26,000 lbs, and in which the vehicle in tow is rated at 10,000 lbs. or less, then you need a Class B CDL. If the trailer is rated at more than 10,000 lbs., and the total Gross Combination Weight Rating is more than 26,000 lbs., then you need a CDL.
If the Gross Combination Weight Rating (the combined Gross Vehicle Weight Rating of the truck and of the trailer) is in excess of 26,000 lbs., and the vehicle is of a type which does not fall under an exemption to CDL requirements (emergency vehicle, registered farm vehicle, military vehicle, or recreational vehicle), then yes, you need a CDL.
Not necessarily, but specifics matter in regard to this question.
That depends on the Gross Combination Weight Rating of the two vehicles, and other factors. If the vehicle is being operated on a for-hire basis, and the Gross Combination Weight Rating of truck and trailer is more than 26,000 lbs., then a Class A CDL is required.
If the Gross Combination Weight Rating (combined Gross Vehicle Weight Rating of the truck and of the trailer) exceeds 26,000 lbs., and the vehicle is of a type which does not fall under one of the CDL exemptions (registered farm vehicle, military vehicle, emergency vehicle, or recreational vehicle), then yes, you need a CDL.
Yes. If it requires a tanker with an unrestricted CDL, so it does with a permit, as well.
For-hire endorsement for non-CDL commercial vehicles (limos, taxis, livery, etc)
For private, recreational use, no. And this applies to all states.
If the Gross Combined Weight Rating of the truck and trailer is in excess of 26,000 lbs, yes.
No, you don't. RVs are exempted from CDL requirements. Your state, however, may require that you upgrade your licence if the vehicle is over 26,000 lbs. GVWR.
Yes, you will need insurance to drive with a CDL license.