You found an solution for your problem. But what's the question?

If you want to know about the range, there's a nice calculator from bosch:
bosch-ebike.com/fr/service/assistant-dautonomie/?setLanguage=10
bosch-ebike.com/en/service/range-assistant/?setLanguage=1

So for 65km and 400hm 1.000Wh is more than enough to drive on TURBO mode all the time, even with 150kg maximum takeoff weight.

Wouldn't it be more useful to use a trailer instead of an cargo bike?
Then you have a very universal bike and can use it also for other purposes than the weekly shopping day.
BOB IBEX: BOB trailers



Or the Topeak Journey Trailer:
topeak.com/global/en/products/trailer




Or you go into sport speed heavy cargo trike pedelec:
https://www.butchersandbicycles.com/