Well, first up ignore the expert comment - I'm enthusiastic about many things, but rarely expert about anything!
I agree with Mike though. 300 is standard in our group, and we use that for multi player games too, but that doesn't allow for the use of a few of the real big guys who at that scale would be over half your force! Upping to 500 gives you far more options for varied formations and access to the full pantheon of living gods among Anyaral.
Sadly, despite having the collections to do so, I've only ever gone larger than 500 at Twilight events - the game fits the role of quick & casual for us and does so well