I've illustrated for stamp companies as well as selling my own images in digital format.
This may not be the answer you're hoping for but I draw by hand, scan it in, and do any minute detail touch-up with my Wacom Bamboo tablet.
I use either Copic multiliner pens or Micron and have used a variety of brands of super-smooth cardstock.
For me, the Wacom works well for touching up and sometimes a little more editing . . . and another beneficial investment is a good light pad if you are going to draw by hand. The Artograph LED light pad is wonderful:
Artograph LED LightPads - BLICK art materials
I can't imagine drawing everything on a tablet or with software - it's just not the way I work. Good luck!