If the property were owner-occupied, would I only receive credit for one rental unit's income, while the non-conforming basement income wouldn't count?

You also get 100 free credits on sign up so great if you just need a smaller list done. 

Then they didn't pay them and the  bad credit goes to someone else! 

I'm broke as a joke but I have good credit how do I get started 

The Heloc can also pose as a debt obstacle since its an open end mortgage a.k.a credit card.a mortgage is also set up over 30 years so it offers a lower rate and payment. 

For example, I mention that every adult must pay a $30 application fee, pass my credit/criminal background, make a combined income of 3x the rent, and whether or not the property accepts pets.

Another option is to co-sign but that has the same impact on my credit and responsibility to the bank.  

Yes, but the 3rd option is I pay the remaining seller note principle in cash via my own savings/lines of credit. 

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

You definitely want to use a thorough screening method like rentprep.com that gets their income, credit, background check, and call at least 3 references (make sure to verify them by address/job and then their name).