I would suggest a multiple server environment, not a virtualized environment. Those two things are not related.
Better than that: The Vicidial Manager's Manual has scaling suggestions. Free Version here:
http://www.vicidial.org/download_survey.php How many servers with each type of role.
There is also an agent manual and PAID versions of both (highly recommended, BTW).
http://www.vicidial.org/store.phpYou may want to have an actual teleconference to discuss this and perhaps pay a consultant. Over 100 agents can become complex, and a consultation (or several?) may allow you to get past the potholes without blowing wads of cash. On launch day, you may even want to have something resembling a babysitter if you can.
I also recommend building your first server and getting ONE agent live with your final scripting and everything in place for a day (or two) well in advance of launch. That can be done with a single server (which would later become your Database server if it's the Biggest Baddest server of the bunch). Alternately, that single-server SINGLE AGENT "proof of concept" system can be virtual. No hardware investment at all. Perfect for a proof-of-concept for a single agent to prove everything from vicidial call pathway to agent script and even whatever money-pathway you have to verify. Well BEFORE launch (as much as possible).