Highest number of units without getting into commercial buidling codes at 4 units you have additional engineering requirements. 

I work with several who go to 600 or don't require a FICO for commercial at all.  

Also, focus on 2 years of job/income stability.Class D Properties:Cashflow vs Appreciation: Typically, all cashflow with little, maybe even negative, relative rent & value appreciationVacancy Est: 20%+ should be used to cover nonpayment, evictions & damages.Tenant Pool: majority will have FICO scores under 560 (almost 30% probability of default), little to no good tradelines, lots of collections & chargeoffs, recent evictions.

Using a HELOC for the down payment on the second home might be an option, but lenders may require you to wait a few months post-closing on the multi-family before approving new loans.The BRRRR-style approach could work if you can renovate and refinance quickly, but make sure the timeline aligns with your lender’s requirements.

The high end is the 20 or so co ops on 5th Avenue or Park Ave (one is on East End Avenue) that require liquid assets of $100 million + to gain board approval.  

Most individuals can originate the debt these projects require as well so its not as if your signature is opening the doors to properties these partners couldn't purchase on their own either.  

BTW: most owners that have hired a PMC, don't want to speak with you, much less meet with you in person to hear a hyped-up sales pitch.Also, you want to do rental arbitrage - so, you will need to be properly licensed to manage properties you do not own as required by your state & local laws.- why would an owner want to do business with someone NOT properly licensed?

However my understanding is that exceptions can be made if unexpected life events happen such as job relocation, eminent domain, marriage, divorce, changes to family size, deployment, imprisonment, bankruptcy etc. 

If you have equity and decent credit, a conventional Fannie Mae HomeStyle (or the Freddie Mac version) would likely be the better option instead of an FHA 203k loan (which will require a 3rd party HUD consultant to oversee the deal in addition to having the contractor involved). 

I understand this is not a requirement, but I have never received a damaged unit from an inherited tenant or any legal issues.