1) Currently there is not any way to record checks with a letter in the check number. To separate the checks in Farm Fund$ try adding 10,000 to each check number for the first checkbook, 20,000 for the second and so on. Then when reconciling the checks will appear like this: 10101 10102 10103 20101 20102 20103
The rightmost 4 digits of each check will be the actual check number and the leftmost digit will be the number of the checkbook.
2) Assuming that the vehicle was setup with Miles as its charge unit, the miles driven are accumulated through farming actions.
Since this vehicle probably was use as general farming activity you will need to set up a fake field to farm with the vehicle and record the miles driven at each fill up. The field name could be "Overhead" and its size does not matter. Farm the field with the vehicle each time you fuel it to record the miles driven. The vehicle enterprise statement will then show the cost and quantity of fuel used along with total miles driven.