At 24 I would keep it simple and pour all extra money into VTSAX or VTWAX until you hit FI (25X annual expenses). At that point you can diversity into bonds or cash if you really want to.
Thanks for everyone's advice, what I am going to do is set up a Roth IRA and a brokerage account with Vanguard and just pour all my money into index funds like VTSAX and VHYAX. Do you recommend any international market funds? REITs? I have a Fundrise account that I have a little money in just to get a feel for it. Any opinions on whether or not that is worth it?
If you are just starting out it might be hard to build a diversified portfolio using the big funds like VTSAX since they each have a 3k minimum.
Option 1: Use a Target Retirement or LifeStrategy fund. The min is $1,000 and these funds are extremely diversified, like ~10,000 stocks and ~10,000 bonds with global diversification. It's a whole portfolio in one fund with the allocations that Vanguard has determined are right for most people with that time horizon, and Vanguard does all of the rebalancing for you. If you are just starting out I highly recommend considering this option. These funds are designed to check all of the boxes for you. Could you customize a portfolio for yourself and rebalance it? Sure, but if you're inexperienced your custom portfolio is more likely to be worse than a Target Retirement fund than it is to be better. I would stick with these for at least the first year, keep learning on the side, and only invest in something else when you are confident. There are a lot of opinions on the internet about which specific funds and allocations to use, and some of those opinions scare me. Don't trust me, trust a company that's mission is helping individual investors make good decisions.
Option 2: If you want to customize, I would use ETFs. As long as you can buy 1 share there are no minimums. The big index funds like Total Stock, Total International Stock, Total Bond, 500 Index, etc. are all available as ETFs. I would read this before building your own portfolio:
https://about.vanguard.com/what-sets-vanguard-apart/principles-for-investing-success/ICRPRINC_042017_Online.pdfBonds: People trash them, not sure why, they serve a couple important purposes. A Target Retirement fund with a far out date, like 2060, will only have 10% in bonds anyway. A 90% stock/10% bond portfolio and a 100% stock portfolio have both averaged about 10% returns going back 90 years. It's a negligible difference. One reason for this small difference in returns is that the 90/10 benefits from rebalancing, selling bonds and buying the stocks during down markets. You can't do that if you're 100% stocks.
To your other questions, yes to international(which is in the Target Retirement fund), but REITs are already included in VTSAX so you don't need to add more. Again, a Target Retirement fund is a safe bet while you learn the answers to all of your other questions... and all of the questions you will have as you learn more.