I’m not even a lender.

In this case, I would need to find some private lender that does unconventional financing (higher interest rate) or I could use an FHA 203k loan.

Go to Pace's group, Creative Financing With Pace Morby, on FB, and look for "gator lenders".

If you haven't talked to a lender yet, that's really your first step. 

Brandon Turner talked about it in his 2nd book, The book on real estate investing, he got a private money lender for one of his first deals from someone he went to church with.

They are all servicer charges and not lender fees. 

There a ton of great DSCR options you can find on the Lenders tab at the top of the page, or connect with an experienced broker who can shop all the best lenders for you and educate you on the best options out there.

We are direct lenders, meaning we lend our own money, for flips within approximately 1½ hours of our home.We walk through every property to avoid surprises and to confirm the rehab estimate.

Never heard of them, is it a hard money lender?

You'll likely want to evaluate the investment with UDFI tax figured in.The Solo 401k trust would make the payments to the seller/lender and would also pay for any investment-related expenses.