No, it is not.
When it is used for commercial purposes.
A commercial vehicle such as a truck or limo needs to have a very high coverage cost because they are used for commercial purposes. The most common insurance for them is comprehensive insurance.
Any vehicle that is going to be used for commercial purposes would qualify for a commercial vehicle loan. You will also have to have commercial insurance on the vehicle.
If your vehicle is being used for company/business purposes, yes.
Insurance follows the vehicle. If the owner of the wheelchair van has no insurance on it, and the person who drives it, has insurance on their own vehicle.... then the wheelchair van would still be considered an uninsured vehicle. Again, insurance always follows the vehicle. The driver who is not the owner cannot use his/her insurance to cover the wheelchair van because they have no 'ownership' or 'insurable interest' in the van.
I have never paid tax for mine
You should have coverages available but your policy is considered secondary to the insurance that is on the vehicle.
The Mercury Mariner is a passenger vehicle. It's only a commercial vehicle if used for commercial purposes. If it has passenger plates, it is not considered a commercial vehicle, and is not subject to commercial vehicle restrictions.
No, you cannot insure a vehicle twice with two different insurance policies simultaneously. This is considered double coverage and is not allowed as it can lead to insurance fraud. You must choose a single insurance policy to cover your vehicle.
You must have adequate coverage regardless of whether or not the vehicle is commercial or not. If you're a business person then insurance upon your vehicles is often a tax deductible business expense so long as you're definitely using the vehicles for commercial purposes.
If you have physical damage coverage on your policy and the cost to repair the vehicle is more than the value of the vehicle then the insurance company will total the vehicle. In the case of a total loss, the insurance company will pay you the actual cash value of the vehicle less any deductible you have. On all insurance policies, where you have physical damage coverage, the insurance company has the option to repair the vehicle, pay the actual cash value of the vehicle, or replace the vehicle. Companies never replace the vehicle.
"Adding Drivers" I presume you mean for insurance purposes? Has nothing to do with ownership (title). So yes.