I work in banking, specifically small business lending. One of the most surprisingly profitable, low-capital companies I've worked with is a guy who does screen printed t-shirts and other apparel. The owner makes six figures in a smallish city with one location (and then proceeds to gamble it all away), and he is NOT business savvy at all.
Success can come in many forms, and many of them don't require a ton of cash — just some creativity and a solid network (which you, as a CPA, may already have).
Edit: On the other hand, another common use of ~$40M is to be an investor in commercial real estate. After a few successful investments, you should be good to go out on your own if that's your thing. This also plays well with the residential rentals you already own.