I stand corrected on the drum brake. The drum brake is only available on the rear if you go with a singlespeed setup. So looks like disc brake on the back if i go with the rollof, and smaller drums on the front.
as for hills, low and slow baby! spin spin spin spin. Let the gears do the work. When descending STEEP long hills, alternate the brakes (front, rear, on off, repeat. ) this lets the brake shoes cool and prevents brake fade.
the most i have carried in a borrowed cargo bike (Workman) was 500lbs. Going up hil using a 20 front 34 rear cog was actually quite easy. Going down i had some brake fade, but as soon as i pumped the brakes it went away. The hill was about a 15% grade, long and curvy.