No. Air brakes are not a factor in determining whether or not a CDL is required in any state. The only instance in which you would need a CDL is in cases where the vehicle is transporting an amount of hazardous materials which requires the display of placards, or when it's a bus designed to transport more than 15 persons (including the driver).
Only if you're operating it on a for-hire basis. For personal, recreational use, you do not.
If it's not a firefighting or first response vehicle, recreational vehicle, registered farm vehicle, or military vehicle (operated by military personnel in the course of their duties), then yes - not because of the the air brakes, but because of the weight rating of more than 26,000 lbs. GVWR.
The air brakes don't matter, insofar as whether or not a CDL is required. As for the GVW being over 26,000 lbs., yes, unless your vehicle falls in criteria for the farm vehicle, military vehicle, emergency vehicle, or recreational vehicle exemptions.
In the US, no - there is no such thing as an air brake endorsement - only a restriction for CDL holders who don't pass the written air brakes test and complete the pretrip and road tests in a vehicle equipped with air brakes, which prohibits them from operating vehicles requiring a CDL which are equipped with air brakes.
Only if it's either hauling a quantity of hazardous materials which requires placarding, or if it's a bus designed to transport more than 15 persons (including the driver).
Only if it's a vehicle equipped with air brakes.
Air brakes are entirely irrelevant as far as whether or not that vehicle needs a CDL is concerned. The only time you need a CDL to drive an RV is when you're operating it on a for-hire basis, either as a driver for hire or as a transporter.
You only need a CDL for a vehicle under 26,000 lbs. GVWR if it's designed to carry more than 15 passengers (including the driver) or if it's carrying hazardous materials in an amount which requires placards to be displayed.
A vehicle having or not having air brakes has no bearing on whether or not it requires a CDL. On the weight rating, New York State has a pretty unique law. While federal law permits vehicles up to 26,000 lbs. to be driven without a CDL, New York requires that an intrastate commercial use vehicle with a Gross Vehicle Weight Rating of more than 18,000 lbs. requires a CDL.
Air brakes are not a factor in determining whether or not a vehicle requires a CDL, in any state or territory of the US, period. The only instances when such a vehicle as you describe would require a CDL would be in the case of hazmat haulers and buses designed to transport more than 15 persons (including the driver).
So long as the weight rating of the vehicle doesn't exceed 26k, yes, with two exceptions - you would need a Class C (minimum) CDL with hazmat endorsement if the vehicle is transporting a quantity of hazardous materials which requires placards to be displayed, and you would need a Class C (minimum) CDL with passenger endorsement if it is a bus designed to transport more than 15 passengers (including the driver).
If the vehicle is parked on a hill and the weight of the vehicle is being held by the parking gear you may find that it will be difficult to shift out of park. I suggest using the parking BRAKE to hold the weight of the vehicle while parked. Set the parking brake BEFORE you put it into park, or at least before you remove your foot from the brake pedal. That way you are having the parking brake hold the weight and the transmission becomes the backup for holding the vehicle. It should be a lot easier to get it out of park then.