[akg_67]

I suggest you do some reading before getting started with investing.

Bogleheads wiki and forum has good information and knowledgeable forum participants.

https://www.bogleheads.org

https://www.bogleheads.org/wiki/Main_Page

In addition, following books will give you good fundamental understanding of why and what of investing.

Your Money or Your Life, Vicki Robbins ...

Millionaire Next Door, Thomas Stanley

A Random Walk Down Wall Street, Burton Malkiel

Personally, 95% of my investment portfolio is in Index Funds/ETF. The other 5% I use as play money that keeps me engaged in investing, finance, and trying out new strategies and investments.

[idoh]

I have all of my investments in an S&P 500 ETF. I've been wondering - should I diversify my ETFs or go all-in on the S&P 500? In other words, go large cap only, or large + mid (and or small) cap?

[akg_67]

You may want to consider reviewing Boglehead wiki link I posted, specially the section about Asset Allocation. If all your investment is in S&P500, you are exposed to US Large Company stocks only. You may want to consider diversifying your portfolio to other asset classes. At minimum, you want to setup 3 ETF/fund portfolio: Total stock market, Investment Bond, and International Equity.

Studies have shown that a 60:40 stock:bond portfolio performs almost as well as all stock portfolio but with lower yearly volatility.