Vanguard has some great funds with very low expense costs. I have some goto index funds from vanguard that I’ve made more than 30% with many times in the past couple decades. Schwab also has some great funds that make the same type of gains with .02% expenses.

I don’t talk to any broker, I do all of my trading online. Vanguard does have a $75 fee when buying their funds from a different brokerage house.

Vanguard, Schwab, fidelity could care less if you hold their fund for 3 months or 3 decades. If you sell, somebody will be right behind you to buy them.

As for investing while you are retired: why not? For me, it’s fun watching your money grow. It’s also fun doing some day trading now and then to make a quick buck.