So, I think the correct answer to the question "I have a 5-figure sum of money to invest" is to just go with Betterment/Wealthfront rather than Vanguard, so that you get diversification between asset classes (whereas a specific index fund will get you diversification within an asset class). If I'd known this when I'd asked the question, I would have picked a better mix of Vanguard index funds, and not hesitated as much with figuring out where to put the money. To be fair, Vaniver basically said this, I just think the links below explain it better, so I could feel certain enough to make a decision rather than let the money burn away through inflation.

http://www.mrmoneymustache.com/2012/02/17/book-review-the-intelligent-asset-allocator/

http://www.mrmoneymustache.com/2014/11/04/why-i-put-my-last-100000-into-betterment/