Nice work building the business. Very impressive.
If you weren't going to touch it for at least 15 years I would say to dump it all into Vanguard total stock market. Given that you will start drawing down the money in three years, however, and given that the stock market is presently at historic highs, I would take a more cautious and more diversified approach.
First I would divide the money into at least three buckets: Bucket 1 (money you will be drawing down within 3 to 7 years), Bucket 2 (money you may access 7 to 15 years out), and Bucket 3 (money you won't need to touch for at least 15 years). How much goes in each bucket depends on your other savings and your expected income in your semi-retirement. For Bucket 1 I would put at least 40% in lower risk bond funds, TIPS (Treasury Inflation Protected Securities) and Real Estate Investment Trusts , and 60% in the Vanguard total stock fund. If you don't have significant savings elsewhere and you're serious about scaling back in three years I would also consider putting some portion of Bucket 1 in a high yield savings account like FNBO. Bucket 2 could be 90% stock and 10% bonds, with TIPS, and Bucket 3 could be all VTI possibly with an extra weighting to emerging markets.
I am sure some here would say that with a 4% withdrawal rate there's no need for the bucketed approach. For me, buckets reduce stress in the event of a market downturn. If two years down the road the market has dropped 20%, Bucket 1 will still be closer to even and you won't feel like you're locking in losses when you start to withdraw.
For the specific allocations go and play around with FutureAdvisor.com. You can enter the amount of money, the planned withdrawal date and they'll automatically recommend an investment allocation and identify the cheapest and most tax efficient funds.
