If it were really pulling in that kind of revenue, surely you would need/want in house accounting/tax.

I'd probably worry less about in-house accounting and legal than I would a lot of other things. Those are probably pretty hirable. Depends on the nature of the business of course. As I noted elsewhere, my more immediate concern would be someone who could handle critical matters if you, your wife, or your child is sick (or god forbid you go on vacation) and there are immediate important matters that need to be dealt with properly.