Back when I was fantasizing about what I'd do if I won the lottery, I looked into family offices a bit and concluded that there's basically no point as far as the investing advice goes. It's still likely a good idea for some of the ultra-wealthy for estate, tax, and philanthropic purposes, but on the investment side? The standard passive indexing approach used by middle class individuals scales in a cost-effective ma…
There is one point you haven't considered: Even though a pure indexing strategy is appropriate, it is not appropriate to use Vanguard for this. At the billion-dollar level, assuming that the index funds had an expense ratio of .05% (among the lowest out there) you would be paying annually: 1,000,000,000*.0005 = $500,000 For that level of expense, you could instead have a one-man office or other service provider that…
Even at 5 bps on a billion, I think you'd be extremely hard pressed to do everything Vanguard does for you for $500K/yr.
I'm at least a factor of 500 away from having to consider this question, but if you told me it would cost me $500K to have one fewer critically important person on my staff to deal with, that would be a good tradeoff in itself.