Investing is on a spectrum, from paying huge fees to an advisor, to using a robo-advisor, to dumping everything into an all-in-one fund, to simple three/four fund portfolios, to something more advanced.
It's really easy to do any of the middle three options. The actions you would take are
1. Create an Investor Policy Statement. Again, this can be simple or sophisticated. It can be as simple as "I want 80% in stocks, 20% in bonds. All domestic (U.S.)" Or it can be a lot more granular - how often you rebalance, where new funds are placed, where equities and bonds go based on which of your accounts is more tax-efficient (i.e. put bonds in your retirement funds). People can debate all day what the "best" policy (strategy) is, but you don't have to spend all day eeking out the "best" - you can go with a damn good, damn simple one. (If you go with a robo-advisor, like Betterment, you'll still lose money to fees - the base fees on $700k at Betterment are about $1000 / year or 0.15%, plus their underlying fund ratios, which are also pretty low. But you'll basically just need to pick the stocks/bonds/cash ratio, and they'll do the rest for you.)
2. Decide where your money shall live (where it is now, or somewhere new, like Vanguard.) Get your accounts created, if needed, and do in-kind transfers (if possible), or liquidate as needed and buy the desired allocation of investments. This can be pretty easy, because if, for example, you're going to Vanguard, they can walk you through each step over the phone.
3. Stick to your Investor Policy Statement.