If you're operating any USDOT registered vehicle, you are subject to regulation by the FMCSA.
If it has a Gross Vehicle Weight Rating over 26,000 lbs. and isn't a category of vehicle exempted from CDL requirements under the FMCSR, then yes.
If it's not a type of vehicle which is exempted from CDL requirements under the FMCSR (farm vehicles, recreational vehicles, military vehicles, and emergency vehicles), then yes, it requires a CDL. It's not the air brakes which make it require a CDL - it's the weight rating.
For vehicles and combinations with a gross weight ratingof 26,001 lbs. or greater, or for vehicles of any weight which are designed to transport more than 15 persons (including the driver) or are transporting a quantity of hazardous materials which requires placarding under the FMCSR, you need a CDL. USDOT registered vehicles which do not meet that criteria do not require a CDL to operate.
Truthfully. If the job required you to operate a vehicle requiring a CDL, you were subject to FMCSR. But it's not just CDL jobs. If you operate a commercial vehicle (if you're unsure, did it have an annual FHWA inspection sticker and IFTA or state fuel tax sticker?) over 10,000 lbs. Gross Vehicle Weight Rating, you were subject to FMCSR.
If it's a registered farm vehicle which belongs to them, then no, although Ohio may still have their own special licencing requirements for them to possess an upgraded non-CDL licence. If the vehicle is not registered as a farm vehicle, and isn't a type exempted from CDL requirements under FMCSR (recreational vehicles, firefighting/first response apparatus, etc.) then yes, they will.
Only if it's designed to carry more than 15 passengers (including the driver), or transporting an amount of hazardous material that it requires the display of placards under FMCSR.
This is a commonly recurring question. The simple answer is no. Nowhere in the FMCSR or FMVSS is there any requirement whatsoever for air conditioning.
Yes. FMCSR licencing requirements are determined by the vehicle - not who owns it. A CMV requires a licenced operator, whether they own the truck or not. The only instances where you don't need a CDL are when it's exempted from FMCSA regulation - for instance, registered farm vehicles, recreational vehicles and motorhomes, firefighting vehicles, and military vehicles. In these instances, states have jurisdiction over what their licencing requirements are for vehicles of this type.
Yes, you will need insurance to drive with a CDL license.
The cutoff is 26,001 pounds--anything above 26,001 requires a CDL, below that does not, unless it's a vehicle designed to transport more than 15 passengers (including the driver) or else transporting hazardous material in a quantity sufficient to require that placards be displayed under FMCSR.
If the vehicle is for commercial/business use, or otherwise does not fall into an exempted category with the FMCSR which makes it not require a CDL (and is operated within the conditions which must be met for that exemption to be applicable), then that vehicle requires a CDL. If it is equipped with air brakes, and requires a CDL, then the driver must have completed and passed the written air brakes test, and must have performed their pretrip and road tests in a CDL vehicle equipped with air brakes. Otherwise, they get a restriction which bars them from operating a vehicle which requires a CDL and is equipped with air brakes. If the vehicle does not require a CDL, then no endorsement for air brakes is needed - air brake endorsements do not exist on US licenses; only the aforementioned restriction for CDL holders.
A limo is not subject to regulation under FMCSR, and does not require a CDL unless it's designed to transport more than 15 passengers (including the driver), in which case, you'd need to add a passenger endorsement to your CDL. In many states, a limo can be driven with a regular licence. Others may require at least a chauffeur's licence. In either case, your Class B CDL should be more than sufficient, but without knowing which state you're in, a definitive answer cannot be given. You need to check with your state's Department of Motor Vehicles (or whatever the equivalent agency is) and present this question to them.