It seems like this would be more on seller side.It’s not a deal breaker for the buyer, just a pain and occasionally a time suck, it absolutely can be an issue when you sell, not something that can’t be overcome but something that can cost time, money, effort, which again is why I’d just much rather be in condos than multi family all things equal, the per unit savings aren’t even that big in large swaths of D.C.

Very true, and a lot of lenders, especially like fix and flip lenders have sort of a "loyalty program" where more deals equal better rates and better leverage. 

When doing BRRRRs OOS, having the right team in place is vital.

So, be sure you are comparing apples to apples in projections, since they are not all created equally! 

It may require you to maintain a specific liquidity ratio over the life of the loan, or maintain cash reserves equal to a specific number of payments, or upon inspection prior to the loan being Funded, Require you to come out of pocket with cash, for instance, to replace the roof because it has more than two layers on it, replace or grind concrete that has heaved, or embark on a program of replacing balconies that have rotted within a certain amount of time, et cetera...

Increase in family size:A Borrower may be eligible for another house with an FHA-insured Mortgage if the Borrower provides satisfactory evidence that: • the Borrower has had an increase in legal dependents and the Property now fails to meet family needs; and • the Loan-to-Value (LTV) ratio on the current Principal Residence is equal to or less than 75% or is paid down to that amount, based on the outstanding Mortgage balance and a current residential appraisal.

The answers are invariably yes for new investors, and usually for seasoned investors too—the reason being that you need to know what you are getting into.There is a second equally important reason, though, especially when buying from homeowners or investors: You can usually get a credit or additional work done based on the results of the inspection report.

I need to confirm with the lender but assume any such "partial" payments would have to be substantial and equal to at least 10-20% or more of the total loan?

The 4 properties will always make more money than the 1 (all things being equal).  

Assessing both macro and microeconomics is vital.