I am looking to buy my first four-plex within the year.

these will be my very first  rental properties.

Find that number out first and try to give yourself a buffer since cost of living will still go up but also will your rents and expenses.

Do they pay on time (all of the time)?

I would not look at it as altruistic though you can donate time money and houses to charities  for that ..  

Owners mistakenly ASSUME all PMCs offer the exact SAME SERVICES and PERFORM those services EXACTLY THE SAME WAY, so price is the only differentiator – and they often select the first PMC they call!

@Stuart @Gregory Schwartz @Chris Seveney Thanks a lot for taking time to respond to my query.Initially when I made an offer to purchase the property, the lender-1 brought so many last minutes after about 10 days into the deal.

This is a PM I put in place on my very first rental, so I've learned a lot of 'what not to do's' since.  

I guess this is your first deal with this partner so based on the inputs i would suggest structuring the deal 50/50 to leverage both partners' strengths.

Thanks for the thoughts and appreciate you taking the time to respond.