I got 43 miles from my 19.2Ah battery at maximum assistance, over this mixed terrain. It was easy.
The battery on my Dahon Helios is rear rack mounted, but the only time this caused issues, was when I attempted to ascend a 45 degree angled stony dirt tracked slope... the motor was game, and I guess if I had a throttle my bike could have ascended some of it, before I fell off after the bike tipped upwards because weight is imbalanced. Luckily, that wasn't a necessary journey. I've experienced difficulties weighing my bike, but will try again at some point.... however, it measured 22.4kg on my last attempt a couple of months ago - that's with numerous soldered on lights, side mirrors, rear rack, mudguards, various mounts, extension bar, 19.2Ah battery, two Oxford lollipops etc. Unfortunately, I didn't weigh my bike before conversion.
None of the OP's bike fold, therefore how about adding 5.6kg BBS01B kit + 3.6kg 19.2Ah battery + about 2Kg of mudguards and pannier rack to this 10kg bike? = about 21.2Kg? A bit less, with a smaller battery. Wide puncture resistant Schwalbe Marathon Plus tyres would increase weight, as could a comfy padded sprung saddle, possibly a replacement swept back handlebar. Looks like there would be more an upright riding position than my Dahon. Again I have no idea if this mini velo is any good to start with, but if the frame is ok, all components could be upgraded, such as the disc brakes. The battery could be mounted to the lower downtube, for better balance. 20" wheels for more torque. Of course the BBS01B's controller would need it's firmware tweaked.
Condition is "New".
www.ebay.co.uk
Steel framed Tokyo bike Mini Velos might be better made, heavier, but no disc brakes:
The Mini Velo takes the tokyobike concept even further. Super compact so it can be easily carried and stored, the step-through frame design and geometry make it comfortable for sharing between riders of different heights. Small 20" wheels are quick to accelerate and make for a fun ride - perfect...
tokyobike.co.uk
I know a rack and mudguards can be installed, because I've seen them on ebay:
TokyoBike Mini Velo - 2 Years Old, Excellent Condition, Urban Adventure Awaits! Dive into urban exploration with this 2-year-old TokyoBike Mini Velo! Why Choose This TokyoBike Mini Velo?. Join the TokyoBike Community of Urban Explorers!
www.ebay.co.uk
Alternatively: The Crusa's kit seems to work well for the OP, therefore perhaps the OP could get the hub motor kit transferred from the Crusa to a lightweight mini velo, while replacing the old rackmounted battery with a downtube?