Do some serious homework on the markets before putting that 500k on the line. Some, but not all, and probably not half of the stocks in the S&P 500 will continue to gain this year. Bonds have run up recently, so they also have more immediate risk of decline / low yield. Also, consider things not so obvious: option selling strategies. Warren Buffet does it, so smart is as smart does.
Yes, tempting to hold in cash and wait for the market correction - if it ever comes.
Inflation eats cash.