As far as the flickering. Correct me if I am wrong, but we can wait to turn on the row transistors until the data string has gone through all the shift registers. That should keep all the LEDs from flickering.
All I can can think of is that the ULN2003A chips have current clamps so they dont burn out the LEDs.
Do I have to design an alphabet?
How do you handle the transistor rows when they aren't in sequential order?