+1 70mm Sturmey Archer X-FD drum hub.
+1 Clip that comes with the S/A hub/wheel will work and is fine.
Your STI brake levers should work fine -- same pull on a drum as for "road" caliper brakes.
Here's a wheel I built on a 20" folder:
PS: if you replace your headset star nut and top cap with a BMX-style "brake cable through the headset" type (Answer makes one model), and route brake cable appropriately, it looks real clean...