Sound card for MIDI (piano keyboard)

My workstation has a P4PE-X which has an onboard sound card which is pretty basic.

I have a Yamaha P200 piano keyboard with MIDI & plan to connect with my PC. I will be using Steinberg's CUBASIS VST 3.0. The idea is to lay down different tracks of music either from a CD, from the internet, or from my head via the piano keyboard and put it all together on the built-in sequencer. Cubasis accepts analog input (eg. mic, guitar, etc.) which would be useful in the future as well.

Has anybody put together a setup like this, not necessarily with the P200 but with any MIDI keyboard?

I'm most interested in what types of MIDI interface/sound cards would be most appropriate for this. I don't need surround for my purposes, 2.1 channels is fine, but are there sound cards or USB MIDI interfaces that will accept RCA inputs. I'm also wondering if using my CD-ROM drive to sample tracks works as well as getting a separate CD player component (DJ calibre).

And lastly, has anybody used the Hercules DJ console?

Any feedback would be appreciated