The bike, the battery, and the motor are all upscale choices (pricey), but I would like to say that you will not be disappointed with any of them. If by M-drive you mean the "hub-as-a-non-hub" with a freewheel, from the urbancommuterstore.com, it is a great selection. Awesome climber from what I've read.
Over the next year, I suspect you will make some experienced E-bikers jealous once they try your rig out. The bike you are outfitting is the type that is typically purchased as the third or fourth project, after years are spent learning what you don't like. I recommend making up business-card size slips of paper with the web-address of this build, that way when you have to keep moving and someone wants to ask a lot of questions, you just hand them one of the cards...
You may also want to investigate the Thudbuster and the Cycleanalyst, many satisfied customers. Heres the link to the factory longtail cargobike thread. https://endless-sphere.com/forums/viewto ... =3&t=32220