Budget? Particular reason you need a folding e-bike vs just a folding bike (not electric)? Just asking because if weight is a big requirement then perhaps you might want to ditch the electric requirement.
For a great non-electric that can haul some stuff, has a Gates belt and a Shimano Alfine 8 speed IGH (and robust tires) I'd check out the Tern Verge S8i (can be ordered with rear cargo rack and probably front spartan rack). I think that bike runs about $2K without the racks. That bike will be fast, quiet and lighter than any electric you will find.
I'd recommend the electric Terns but they might not meet your weight requirements. They will be heavier. All of the Terns pretty much fit riders up to 6'4" according to their marketing. If you can wait, the 2019 Vektron will be greatly improved over the current version. With like 3 different options of motors and config and more robust cargo capability. But I bet they won't be released until next year. They also currently have at least 1 Bafang option I believe that will probably be a bit easier on the budget and perhaps lighter vs the Bosch variants.
You are definitely correct that 20" wheels make a huge difference in portability and ease of storage. I have 20" Terns, a 24" Tern and regular 27.5" and 28" wheeled bikes. The 20" wheels are awesome if you have to carry the bike up/down stairs or load into a vehicle. If I could go back in time I wouldn't have bought the Tern with the 24" wheels. It is a great bike but I prefer the convenience and portability of the 20" wheels.