There are big hurdles - the vegetable oil. I have been trying to figure out how to get oils on my own. Rapeseed has to be crushed to get the oil... have you seen how its done ? Google it. Its really labour intensive. Imagine the work to get 1 gallon of oil. Not to mention work in preparing, tilling, harvesting and sorting chaff.

The second part - the biodiesel generator requires alcohol and other chemicals. Alcohol requires its own process, where you have to grow a ton of grain, potatoes or fruit. Again, the preparing, tilling, harvesting and sorting, then the Alcohol brewing process which is a time consuming job.

None of this work can be automated... because you don't have gas to run combines and tractors. It will be with horse or human power, like the Amish

...I just don't see how to do this practically in a reasonable amount of time

My proposal is to use woodgas. You need a closed pot to burn wood, a pot with wood chips to catch tar and particulates and an old radiator to cool the gas. Then it can be connected via hose to a 2 stroke/4 stroke. There's a lot of DIY videos. Wood is easy to get, no planting, harvest etc required

Either that or solar and an electric car, or a bicycle