There are not traditional DSCR lenders that would do that.

Maybe a mortgage lender can chime in.

Since you are on the Austin forum and stated you are from Texas, I would be happy to get on a phone call or have coffee with you to help you focus on the task ahead.However, let me remind you, I am neither a real estate agent, or lender.  

I've talked to a ton of lenders and if they know it's an investment property, you're looking at 15-20% down minimum (non owner occupied).

Any lender should be able to easily do a HELOC for you (provided your credit is OK), but a local credit union will likely give you the best deal. 

Do you mind sharing the name of that type of loan/lender that allows you to have the seller carry on a second position?

Maybe they are offering financing because no traditional lender will lend on the building. 

Also, in order to get financing the lender wouldn’t allow SCI to dramatically overpay or they wouldn’t meet the debt service requirements.

During this renovation period would you, as the lender, want an Actual Cash Value or Replacement Cost policy in place?

or market to Lenders for refi's ?