Who, lil ol' me?
Firstly, considering the amount of power you are adding I assume you ARE using a licensed electrical contractor right? If so - they already know what you need to have done and can explain it to you... Something like this is NOT for DIY!
As Sidehack said, assuming you are getting wye (aka star) incoming service then you will already have 240VAC from each phase to the Neutral so that part is fine.
If the incoming is delta then you will need a transformer to change that from the 408 delta to 208-240V and gets a little more complicated: If you do not need any 110v service then the transformer can be for 208-240V phase-to-phase with no Neutral connections
From the incoming service entrance, split off into a few main 3-phase feeders @ around 250-500A each to feed distribution breaker panels filled with 20A breakers. As for balancing, as long as the breaker panels are mostly used only to feed miners and all breakers are same size they will balance themselves out as you add breakers. The slots go L1, L2, L3, L1, L2, L3, etc.