Verified answer

Most brokerage firms require a minimum deposit in order to open an account.

E-Trades new clients to deposit $500 when they open their account.

This $500 has nothing to do with your total assets or your net worth, it is the amount you must submit to the firm when you open the account. It can be used for purchases and will be included in your account balance going forward.

Have to have for what?

You really should not have a brokerage account without at least $5000 and ideally $10k+.