At the current scenario, without knowing anything about you or your properties I will recommend either to look at a loan from your assets using DSCR loan.

Its great that the seller is will to carry a note in a seller 2nd as well, that will help reduce your require monthly payment with the right lenders.

It is more complex and has added requirements such as a formal set of books just like a corporation. 

.- If you decide to have an LLC for each property, creating a Management LLC that all the other LLCs "hire" to run their books, will allow you to only require a bank accont for the Management LLC.2) You may not be able to do a Trust.

I may be able to STR a spare bedroom but that would be for later.Background: A fixer upper, but I do not know how much fixing is required. 

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Given you and your investor both have experience in different areas, I’d say keep a flexible approach and compare city requirements before putting too much money down.

Do you have any recommendations or advice to share?

For example, a property in San Diego may lose $500 per month ($6,000 per year) but gain $60,000 per year in value, making it worthwhile to "lose" money each month in exchange for long-term gains.I recommend you start with BiggerPockets Ultimate Beginners Guide (free).

I recommend you make a video of you entering the unit and documenting exactly how it is found.