I reckon the Virus is excellent for part 'backbone' of a setup. ...Meaning, although the Virus is very good indeed, I don't reckon you could rely on the Virus for all your sonic needs.
In addition to the Virus, maybe add a rompler to that (ie. Triton/Motif/Fantom, or a VSTi of the same/equivalent nature, etc.) so that you can add more general instrumental sounds, such as piano and other multi-samples of 'real' instruments, and most definately add a sampler of some sort (hardware or software) for your sampling and drum requirements, and possibly maybe another virtual analogue variant (hardware or software), eventually, for a more diverse and complimentary analogue/synthesis sound that sits well alongside the Virus.
If you want to add real instruments (like vocals, guitar, etc.) then you'd also need a mic or two, and a pre-amp to go with it (via either a dedicated pre-amp hardware unit, an external mixer, or occasionally via a pre-amp input on a soundcard).
Depending on whether you either take the software or hardware route (or even a mixture of both), if you then have a number of hardware units, you might then need a mixer for routing signals to and from sources (including outboard effects and processing, and the like, should you so wish) and/or a multi-input soundcard to mix and record multiple sound sources at any one time, and you might need a 2in/2out or 4in/4out MIDI interface to control your synths/sampler at any one time. It depends on what direction (software OR hardware) or blend (software AND hardware) you wish to take.
Hope this helps, best of luck!
Timo
