Have you read "A Random Walk Down Wall Street"? It's now in it's 11th edition, and has been an investment classic for laying out theory backed by academic studies and decades of stock market history.
Nice thing about Vanguard is how hard it is to pick an expensive fund. Vanguard's philosophy is to save the investors money - doubly so since the investors are also the shareholders of Vanguard. Most of the investment world doesn't have those interests aligned, so be careful out there.
Is this "down payment on a house" money or "4% of this covers our expenses" money?
If it's $150,000 range maybe an all in one fund is okay. Not great, but it's easier than having several mutual funds.
But once you get past $750,000 range, you're looking at a significant bond allocation in a taxable account. It might make sense to divide things into several funds, and even look at tax-exempt bond funds.
One vital caveat: are you inheriting an IRA? If so, STOP! Read about inherited IRAs first - you could easily make a mistake that costs you a lot in taxes. IRAs can be "stretched" over your expected lifetime, where you'll be withdrawing money each year. You'll need to read up and get advice if this is your situation - if you are inheriting an IRA.
