I've done a number of owner finance deals as a buyer, and an attorney is not terribly expensive, typically about $1k per property including the note and title search. 

He currently has about $10,000 cash and about $20,000 in credit "Home Depot line of credit for materials."

The catch: my partner just sabotaged his credit and is self employed.

I get these lines of credit/ mortgages off my investment properties that are rented.

I was planning on purchasing a 400k MF with cash but was planning on getting a line of credit on the piece in order to handle any "expected" surprises. 

Also, it would be wise to get some credit lines just to have in case as well. 

I have little income with good credit.

It will most likely be a line of credit with a second lien deed of trust (2nd mortgage).

As long as your partner has good enough credit and documentable income, and assuming that together, you both can qualify for the loan, then it is possible to purchase the house this way and basically house hack. 

I didn't have a good down payment, but I do have good credit & a higher personal income, so I was able to acquire a large enough personal (signature) loan to buy with "cash."