@concoa I believe I know what you are asking and I posted the same or very similar question a few days ago. From my understand, the answer to questions 1 and 2 is Yes, provided your total contributions added together don't exceed the annual maximum limitation. Not sure what that is but you can do a quick search.
I believe question 3 is the same thing I asked in my post. I've found conflicting information as to whether you can have both a SEP and a Solo 401k owned by the same business. From my research, your business can definitely have both provided you use a prototype SEP plan agreement other than Form 5305-SEP that explicitly permits both plans to be maintained simultaneously.
It's also my understanding that you can make employer contributions and employee contributions until your tax filing deadline, including extensions. The Solo 401k must be opened by 12/31 in order to make contributions to it in the previous year (i.e. opened by 12/31/22 in order to makes 2023 contributions that can be deducted in 2022).
I made the mistake of opening a Solo 401K with Fidelity with an existing SEP 5305. I've made a total of $4000 employee contributions for the previous year and I'm not sure how to rectify this. I could probably contact Fidelity and have them attribute them to 2023, BUT I need more deductions for 2022. So, I'm trying to find out what I need to do to allow this.
I was hoping to get some advice here, but I think my best bet is to schedule an appointment with a financial advisor.
Hope this helps, but be sure to confirm what I've said!
