aballen, there are 20 pins you can use as digital three-states, so you can get up to 20*(20-1) or 380 LEDs charlieplexed. The challenge is routing: you can't fit 20 traces in a 20mm wide PCB, unless maybe if you had four layers and really tiny vias. Gotta do some things serially. There are SMD versions of the 74HC595, aren't there?