There is still no guidance regarding what costs are included as "transportation," other than gas for business vehicles, which was indicated in previous guidance.
It appears that vehicle and equipment leases will be considered eligible rental costs if they were in place prior to Feb 15, 2020 (because they are personal property)
No, prepayment is not an allowed use of the PPP and is not eligible for forgiveness. Also mortgage principal is not allowed.
Any interest paid on mortgage on property used for business purposes is an eligible expense that the PPP can be used for, and qualifies for forgiveness. This includes auto loan interest on a car that you own to make business deliveries. You will need to review your monthly bills, or get a copy of the amortization schedule from your lender, to determine the interest portion of the payment.
Yes, rent for business property like this is an eligible expense if it is paid or incurred during the covered period.
There are consequences of spending on unallowable expenses, including needing to return funds used for these unallowable purposes. If done knowingly, this could be considered fraud with certain penalties.