I'm about to start investing at 23. I have about $9k in savings and I'm thinking about putting $5k of that in a standard Vanguard index fund (all stocks, no bonds). Is there anything wrong with this plan?
A coworker showed me an alternative to Vanguard called Betterment, but its 0.25% fee seems bad.
Do you plan to use the money to start your retirement fund? If so, stick to your plan, but first open an IRA at Vanguard (it's free), then invest the money. I'd suggest a Roth IRA given your age and likely income level. (See the OP for the differences.)
If you just want to get the money off the sidelines, then yes, it's still a good plan so long as you don't intend to use the funds in the near-term (due to short term stock market volatility).
Don't take your coworker's advice.
How do you decide to split retirement vs. non-retirement savings? Right now I max a Roth IRA and contribute 8% of income (2% above the match) to my Roth 401K, but I also try and save on the side (in addition to having an emergency fund). People often say max the 401k before you save anything else. Seems like it would mean I wouldn't be able to put a down payment on a house...
This will be squishy, but it kind of comes down to how much you can save, how old you are, what you are saving for, what your priorities are, etc. My own investment strategy was to work on filling several buckets (retirement, savings funds/non-retirement savings, and kids college funds) all at once, to varying degrees, rather than focus on one at a time. Initially we couldn't save much, so I set the mix based on our age and the priority my wife and I put on retirement. That ended up being roughly a 70/20/10 mix, respective to those buckets. Over the course of many years, we got comfortable with the level of savings we had, and stopped adding to the fund (letting it just keep churning dividends), directing what used to go in there to our IRA's.
I don't think it's a good idea to focus on retirement at the total expense of other priorities, though I personally put that at the highest. Just find a mix of regular savings into those buckets that you are comfortable with, and which will advance your goals (saving for a house, for example).