I disagree with some of the Boglehead stuff, but the wiki is a good resource.
You don't need to do any trial and error. You just need to pick some funds and hold onto them for a long time. The funds Betterment has already picked for you are probably pretty good.
(In fairness, they do some other stuff which is more value-added like TLH, which is more work to do yourself, but again, it's hard to justify the 0.25%.)
"If You Can" by William Berstein is a good, short ebook on this subject.
I got the Wealthfront pitch when I started with my employer, but I feel much better with my current arrangement. Your comment "I have very little choice but to stay put" is never nice to hear in any context, so I hope you can move along from that place.
http://www.cnbc.com/2015/06/16/is-your-advisor-a-fiduciary-c...