The advice for which index fund is pretty consistent. It used to be S&P500 index fund but it is now all-market fund or even all-international-market fund. But t

The advice for which index fund is pretty consistent. It used to be S&P500 index fund but it is now all-market fund or even all-international-market fund. But they are all fine with minimal differences. The answer to when is always. Avoiding downturns is timing the market, it can't be done reliably. It is worse to mistime the market than to stay in. That is basic principle of passive investing. Trading between cash or mutual fund is not passive investing but active. My feeling is that investing emails will be low cost to send out but will be high support. If you have better strategy, make your own mutual fund.