Form 5500 EZ for Self Employed 401k and Sole Proprietorship

I apologize in advance if this is the incorrect subreddit. Please redirect me where needed. I have been searching for some answers in regard to appropriately filling out a Form 5500 EZ. My family tax “specialist” doesn’t deal with 5500s. Ugh. And then contacting some other local guys was met with the same hesitation.

1. Business activity for those who do part time 1099 work in healthcare? I assume it’s one of the 621xxx codes even though the family member doesn’t have per se an office as an independent contractor.

2. Plan characteristic has to be one of the 2x codes since Fidelity states it’s a defined contribution type of self employed 401k plan. Is that correct? The employer only contribution is variable based on what is produced part time (20-25% of gross). Their part time W2 job is where they do a full employee contribution for a small match. 2D, 2E…?

3. Is the employer contribution amount what is only in the 2025 tax year filings or does it include 2024? Plan was opened in Jan 2025, a small amount from 2024 work (noted on that 1040) was deposited before rolling over an old 401k into it. Then for 2025 filing recently, some more put in. The AVS mentions only the deposit date and not the tax year assigned to contribution. This is a bit confusing about what goes on the employer contribution line.

The form otherwise seems straightforward. Helped to get an EIN off the website since the plan now exceeds $250K. Happy to answer any questions to clarify things. Thanks to all!