Having just put an electric wheel (Geoorbital) on a folding bike (Montague Swissbike X50), I'll agree that weight is a serious consideration.
While I'm looking forward to riding to work, and am feeling confident enough that I'm not going to bother with a test ride, carrying the bike up to the second floor is going to be a bit more of an effort than before, exacerbated by the bike now being markedly front heavy.
Your design with the motor at the bottom bracket (if I'm thinking of the correct Bosch system) would help with that, as would the in-tube battery.
As a counter-point, I'd suggest looking at other folding ebikes such as the Montague with the Superpedestrian Wheel:
https://www.montaguebikes.com/produc...lectric-bikes/ or with the Zehus Hub motor:
Montague Electric Bikes - Boston ZE
Montague Swissbike X50 with Geoorbital Wheel.