Worksman could probably upgrade the bike to the 3 speed / coaster that they offer on the tandem model... my experience with Worksman bicycles has been very good as I own a cargo trike and my friend has a cargo bike and they make some pretty bombproof, albeit heavy frames.

To add front brakes you would either have to get bosses brazed on or swap the fork to one with brake mounts... with what looks like some pretty long reach I'd look to run V brakes for increased stopping power.

Another option would be to buy a Raleigh 20 and upgrade the wheels to alloy and either have v brake mounts added or look at hub brakes which would be a good idea in Seattle... hub brakes are also available for the Worksman and the if the folder was orered with the tandem wheelset you'd have a coaster rear with a 3 speed and a drum brake up front.

Wondering what Worksman would want for the tandem wheel set alone as this would also serve as a nice upgrade to a lot of 20 inch folders like the Raleigh 20.