Does your Fidelity account have a total stock market plan. Vanguard's VTSAX is a low fee index fund version of their ETF VTI. Tracks within a few cents or so of VTI, and probably has a few clones by similar names. Otherwise, look at how you want to be positioned:
Large Cap is your big companies, usually with lower returns, but probably with decent dividends, so they actually do pretty decently.
Small Cap are your growth companies. A lot more volatility, a lot more up, and a lot more down when the days are bad, but usually perform pretty well during the good markets
Mid Caps are somewhere in between, and may have some dividends, and more volatility usually than Large Caps, but not as crazy as Small Caps.
I think it makes sense to fairly distribute for an mildly aggressive portfolio. Something like 30% Large, 30% Mid, 30% Small and 10% International. If you want to go for more growth, ratchet up the Small and Mid a bit and lower Large cap. International is a rocky road right now, but you should aim for 10-15% because it will pop and it's good to have some eggs in a world basket.
As for bonds. Yield is still shit as the Fed is keeping rates low. I've never been a big fan of bonds anyway, and right now I'm really not interested in owning any.
Your instinct is also dead on. Keep those fees low. Don't look at past performance and think it's indicative of future performance, and... Don't freak when the market swings (not that I think you will). Remember, time in the market always beats trying to time the market with long term investments.
Oh, and target accounts are not horrid during rocky years. I have a test account, just about $20K, sitting with Fidelity in a year-target account, and although it's been a low percentage performer during the last few skyrocketing years, it did slowly tick up at a decent rate. It's also doing really well right now with the downtrend. I actually am even on that account right now for the year, which is pretty amazing. Now, once things snap back, we'll see how it performs against its big brother.