Be sure the individual 401(k) plan you choose has the features that are important to you, such as Roth contributions, IRA rollovers, or 401(k) loans. For example, if a 401(k) loan is important to you, Fidelity, Schwab, and Vanguard don’t allow them with their plans, but it is an option with eTrade.
How to Set Up a Solo 401(k) and What Plan Features Should You Look For?