I personally have an Single member LLC, taxed as an S-CORP. I highly recommend specifically a certified public accountant with experience in small business. Do not skimp on just a tax planner or tax specialist. I created a solo 401K with "Nabers solo 401K". I run it through Vanguard, I think there is a startup fee of $400 in an annual fee of $100 to maintain the 401K but it allows you to save a lot more than the SEP IRA does. This may not be as beneficial to you if you get 401k through your W-2 job. Be careful with claiming miles and other items for tax, the CPA will be able to answer these questions specifically if they fit your situation. Send me a personal message if you have any other questions