I structure all my personal relationships around B2B SaaS contracts. Mom isn't happy when I make changes to the ToS but I've got pretty hard vendor lock-in and a defensible moat there, so I mostly don't worry about the reputational damage.
You almost certainly want to have a partner you can depend on to backfill and probably a few people who you have vetted and aren't just a relatively anonymous email. I don't really buy that it makes sense to just be a single-person company at that scale even with external services.
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.
So every individual becomes a company? The natural tendency of capitalism is to create bigger companies for "scale". Even if it was possible, what exactly would be the benefit of one person companies?