1. What are additional vCenter Modules?
-> vCenter Update Manager (a.ka. VUM)
-> VMware converter
-> VMware guided consolidation service
these modules may be released separately, install on top of vCenter, and can be upgraded separately.
2. How many hosts & VM you can set up on MS SQL Express Database?
-> 5 hosts & 50 Virtual machines or maximum DB size:5GB (Source RTFM Videos)
3. What are basic processor & memory requirement of ESX4.0?
-> x64 Processor and 2 GB minimum RAM
4. What are CPU,Memory,Disk & Networking for vCenter?
-> 2 Sockets 2GHz
-> 3 GB RAM (Add 1.5 GB if Web service is also installed)
-> Gigabit NIC Card