Size of paper doesnt matter when posting your comic- as long as it fits Tapas' upload requirements(940 pixels wide x 4000 pix long- 2MB). So you could use whatever size paper you need.
Me preferably- when working traditionally, I use 11" x 17" bristol, coz I work with mainly quills/nibs and brush(some tech pen as well). Regardless of pencilling/inking traditionally or digitally I always color & letter my work digitally.