@RevolverRob,
These folks in Eugene, Oregon make pretty great commute and cargo bikes and they are super helpful on the phone and via e-mail.
https://www.bikefriday.com/folding-b...ric-cargo-bike
https://www.bikefriday.com/folding-b...-city-commuter
I have test ridden several of the all-manual cargo versions, and intend to have one someday before I age out.
The owners of the local St Paul dealership routinely use an e-cargo bike year-round to get their stuff and small kids up and down the river bluffs and into south St Paul,
which are similar in grade to some of your downtown Seattle routes.