Realizing that I had little knowledge about electronics, and without the ambition to become an electronic engineer, I decided that the easier way was to use a ZERO motorcycles bike as donor for my project. The only electric-related problem would be to lengthen some cables. :-).
Starting from the trellis frame with custom battery pack that I created, I evolved to a sheetmetal rivetted frame into which the ZERO battery pack would fit. To keep the design clean and the front very low, a new front suspension system was constructed (Hossack style with upper pivot and lower linear slider). Also the design has changed into something more practical with no more holes in the side. This eliminated also the need for a central stand that can be activated when seated.
Well done! One of the cleanest layouts I've seen in a very long time & well worth developing to a finished product. I look forward to further details.