Late Form 5500-EZ & Successor Plan Rule

Edit: I’m happy to pay a professional to advise on how best to navigate the situation I’ve described below  Would anybody here be willing to take this on? Or be able to refer me to somebody that can? I’ve reached out to a few professionals and unfortunately have not had any luck  Thank you.

Hello, I am self-employed and have been contributing to a solo 401k since 2022, but I think that I’ve made some mistakes that I need help resolving.  I've asked my CPA and his 401k plan administrator, but they are unsure of how to help me.

In January 2022 I opened a Traditional Solo 401k and Roth Solo 401k at ETrade.  When setting up the accounts, I used Plan Numbers 001 and 002 as directed by ETrade.  The Plan Sponsor was my sole proprietorship.  I made zero contributions to the Traditional and $3,000 to the Roth.

A few months later I decided to establish an S-Corp, and I opened up another Solo 401k account at Vanguard with the S-Corp as the sponsor.  For this account I used Plan Number 001.  Since I didn’t plan to operate the sole proprietorship any longer, I closed the two accounts at ETrade and rolled the Roth 401k balance into an existing Roth IRA that I hold at Vanguard.

I am now realizing that I should have filed Form 5500-EZ after closing the ETrade accounts.  I am also wondering if I may have violated the successor plan rule by erroneously considering the sole proprietorship and S-Corp to be separate employers rather than an affiliated / controlled group.

Questions:

1. Will I need to file two separate late returns using Form 5500-EZ and pay the associated $1,000 in penalties for the ETrade accounts that were closed?  Or is it possible that I may only need to file one considering I made zero contributions to the Traditional account?
2. Do the sole proprietorship and the S-Corp qualify as affiliated employers?  If so, did I violate the successor plan rule by opening the Vanguard 401k within 12 months of terminating the ETrade accounts?  What penalties would this incur and how would I rectify this?
3. If the sole prop and S-Corp are affiliated, do I need to amend the plan sequence number on my current Vanguard solo 401k account to be 003?

Added an edit to my post to clarify that I’m looking for professional assistance. Would love to work with anybody who is willing to help. 

Oh man, I'm in a similar boat to you and it's stressful. Long story short on mine is Schwab stopped offering the roth option when they bought TDA so I had to move. My plan got "terminated" rather than migrated (not sure of the correct term) to Etrade. I selected plan number 003 and 004 (now it's set to 003 for both). But the advise I've gotten was to file the 5558 by tomorrow with my original 001 plan and work with an ERISA attorney or TPA in the 75 days of extension. I paid for solo401.com in an anxiety filled rush to get some advice and the goal would be to move my plan to eventually to not deal with this stuff again - including every 6 years needing to update the plan docs which I just learned. To me for 1, it sounds like you would file one 5500 because the plans were connected. 2, given they are under two different companies and I don't think you have an issue with succession. 3, I would stick with 001. Obviously not professional advice but that's what I'm thinking from what I've learned but I could very well be wrong. If you find a good attorney / advisor please let me know though! I'm having issues finding one myself.

Taken from the 5500-ez instruction: 

"You do not have to file Form 5500-EZ for the 2023 plan year for a one-participant plan if the total of the plan’s assets and the assets of all other one-participant plans maintained by the employer at the end of the 2023 plan year does not exceed $250,000, unless 2023 is the final plan year of the plan. For more information on final plan years, see Final Return, later."

Why would you not start a traditional IRA or Roth IRA? If you aren't exceeding the limits for IRA's?