It should not mater if you use common cathode or common anode as long as the circuit is designed accordingly. I guess you should decide do you want to turn on a segment with a 1 or with a 0.
If you run out of I/O you might consider a chip like this "16-Bit I/O Expander":http://search.digikey.com/us/en/products/MCP23017-E/SO/MCP23017-E/SO-ND/894271
If you run out of I/O you might consider a chip like this "16-Bit I/O Expander":http://search.digikey.com/us/en/products/MCP23017-E/SO/MCP23017-E/SO-ND/894271
