However, it seems that few people if anybody is factoring in the increased non-payments into their pricing as they would if their vacancy rates crept up.  

Did you factor in the estimated $4k-$5k in closing cost as I assume you are doing conventional financing? 

Dodd-Frank specifically lists this statement as one of the five factors a lender should use when deciding whether the loan is for a business or consumer purpose.

It depends on a variety of factors, including the strength of your justice system.

The number one factor of what you buy is how much capital you have access to...that means its a combination of purchase price, location, condition, and availability of inventory...I would add these as metrics alongside the cash flow.

Another less-ideal factor is that if I buy these on one loan (as may be necessary to meet minimum deal size) then I will have them forever linked, even after I refinance, unless I pay off the loan.

There are a lot of factors, but you may need to start with a DSCR loan, which looks mostly at the amount of income from the units vs the mortgage.

Given these factors I would wager a guess of around $2300-$2500/month in rents, however with a 5 bedroom home in one of these areas it can be very possible to get that in rents without having to go to the headache of rehab.

Each turn means more wear and tear repairs (not reimbursable through security deposit) so factoring in higher repairs/turnover costs could be worthwhile.  

Be very professional in your presentation of the information and avoid trying to influence or oversell items.