26,000 lbs. is what the manufacturer rates it at. So long as you do not let that vehicle get over a gross weight of 26,000 lbs, you do not need a CDL to operate it.
The only times you are required to have a CDL for a vehicle under 26,000 lbs. is when it's carrying a sufficient quantity of hazardous materials that placards must be displayed, or if it's designed to carry more than 15 persons (including the driver).
If you're attaching a trailer to this 26,000 lb. truck, then you are creating a combination which is rated at over 26,000 lbs. GVWR, and will need a CDL with air brake allowance - Class B is the trailer or vehicle in tow is rated under 10,000 lbs, Class A if the trailer or vehicle in tow is rated over 10,000 lbs.
Air brakes are not a factor in determining whether or not a vehicle requires a CDL, in any state or territory of the US.
Air brakes have absolutely ZERO determination in whether or not a vehicle requires a CDL.
No. Air brakes are not a parameter in determining whether or not a vehicle needs a CDL.
Only if it's a vehicle equipped with air brakes.
Not unless it's a bus designed to transport more than 15 passengers (including the driver).
Only if it's a: transporting hazardous materials or b: a bus designed to transport more than 15 persons (including the driver).
To answer you we need to know what country's traffic regulations you are asking about.
Only if it's transporting 16 or more persons (including the driver) or sufficient quantities of hazardous material to require placarding with HAZMAT warning signs.
Yes
No, unless you're hauling something which requires a hazmat endorsement, such as contaminated soil.
Whether a vehicle has air, hydraulic, or air-over-hydraulic brakes has zero determination on the class of license required to operate it.
The air brakes are irrelevant. And you'd need a medical card in that instance if you were doing interstate operations, but not intrastate operations.
Only if it's hauling hazmat or is a bus designed to transport more than 15 passengers (including the driver). Air brakes have absolutely nothing to do with whether or not a vehicle requires a CDL.