I wouldn't look at expenses per door, expenses as a percentage of gross potential profit.Per door is mainly acq cost and rent...

@Tanner Micheli, wherever you try to BRRRR, the numbers would still require you to (all-in) bring it up to ARV standard for no more than the percentage of ARV that your Lender (using their appraisal) will lend you.

What is the standard percentage down hard money lenders require & are they going to run a credit check? 

Obviously, high percentage credit cards are good to get rid of, but these other areas are up to individual desires and timelines. 

If I negotiate seller financing, I am afraid to get into an agreement with any kind of balloon payment (just because it makes me nervous to have it hanging over my head) but I would like to negotiate a lower percentage downpayment than 20% so that I could afford to purchase all four (rather than two) under a warranty deed contract.

Keep in mind that interest rates appear to be rising, if your rate resets in 5 or 10, consider that an increase in a few percentage points may do to your debt service.  

I have found that this increases the percentage that the borrower might be able to start making payments again. 2) I have a list of specific states that I buy in and don’t deviate from it.

I know it could be a commission based percentage , flat fee, or combo of both.

I've seen many different forms of promotions to get a renter to sign early; gift cards, percentage off of rent, or something like a small deposit for a pet, etc. 

The profit gets divided on a per basis percentage.