Unless your coffee van is being run out of a semi trailer, I cannot see how you could get anywhere close to enough panels, and even if you could, cloud cover can take you offline in an instant.
I can't see it being feasible to tap off the landowners power either. In most cases the power outlets that you can access will be rated for 10amps, when your setup would need a 20amp. If you were to plug into the landowners outlet and trip their circuit breaker (or worse) I doubt they would have you back!
Honestly, I think your best bet is to engage a professional for your fit out.