Most banks will limit the income credit from the rental given your limited ownership (less than 2 years).  

I currently have a potential tenant who makes good income and everything seems good about her, however her credit score is horrible (about 450) and many derogatory credit accounts.

I've decided to do them in the order received and process until they no longer qualify before moving onto the next and making them pay the credit/background check fee.  

I've contact Commonfund, Solvay Bank and Prime Lending...seems the best rate for a sfr investment is 6.1% with 760 credit score and $100k+ income, $100k+ in bank and we are renting for $900/month.Is this the best I can get?

I did try a few local banks, but they want to use my personal income and credit score for loan decision rather than asset based.

A line of credit to use if I need it. 

It might mean you lose the deal, but it might also save you if something terrible lurks. 

These are typically built with some type of government subsidy or incentive such as tax credits for the developer in exchange for the leasing restrictions.

I'm eager to build business credit.

Particularly someone who I could open a line of credit with to make it easier to fund the repairs on projects without tying up my cash.