If I recall correctly you can feed each dimming module with 4 circuits if you wish. I would at least install a raceway from the panel to the dimming module to allow for more circuits to be pulled to the module down the road if the need arises.
BTW, the system I installed had 5 Masters and around 10 Slaves. BIG house and this was a retrofit install. I had two weeks to get it down while the owners were on vacation. Like you, the owner of my shop took the install & programming class instead of me.
I really like the flexibility of the system. We integrated the Vantage system into his security and HVAC system. In the event of a fire alarm signal at the security panel the Vantage system would turn on most of the lighting inside and outside the house to allow for easier egress.
