agniusm wrote:20" running front, 24" with HS3450 rear. At the moment i am coming at 2600mm in lenght (bullitt 240).
With a long wheelbase like that along with varying front loads so the CG can change pretty drastically I'd copy the front end geometry of a proven bike as similar as possible. Since it's going to be electric and probably have typically higher speeds, I'd add about 1/2" of trail. The geometry up front is going to be critical enough that I would even design the headset connection so that if I didn't like the handling I could easily cut it and weld it at a different angle.
I had to do that on my cargo bike. The head angle was too steep at first giving it too much sensitivity to changes in CG, especially at speed. I hacked it off and slackened the head angle. I went a bit far resulting in a trail of about 4", but I've lived with that because it tracks so well at speed. It's pretty sluggish resulting in some weaving at very low speed, something you won't want on yours, since it sounds like more of a cargo hauler.
Are you able to test ride any cargo bikes? If so, test at very low speed as well as going down hill. Copy the geometry of the one you like best, or at least the handling differences will give you some direction.
I can't wait to see what you come up with. I've been dying to do a bak fiets, so maybe you'll come up with some stuff I can borrow.