Well, still only learning myself but i think this is correct;
Yes the kit seems like it will help to do CCNA but to do CCNP i think you will probably need a couple more routers to fully setup routing protocols effectively.
As for the question about plugging it into the Internet, you will not be able to use it for ADSL because it doesn't have an ADSL WAN interface, as for cable, i am not sure. I think you can because the ethernet interface will just plug into the Cable box but i have never used cable so don't quote me on that.
Cheers
Wayne