True off market deals are ones that you find yourself, direct from the seller without a wholesaler or any other middle person involved. 

Each unit is individually owned, with some owners holding multiple units.A few things I’m trying to understand better:Pros and Cons: What are the main benefits and challenges of owning multiple units in a property like this with a condo setup?

you should be calling an attorney if what you've said above is true. 

But to sum it all up my new jersey properties where slightly out preformed by my out of state properties and it took longer for me to really be able to enjoy true cashflow from my NJ properties. 

Depending on where you are looking, inventory for 1-4 units can be a challenge as a lot of the NW suburbs are all single family homes unless you are further NW like Rockford or Elgin or something like that. 

Challenges?

Everyone's obsessed with "off market deals" but a realtor who knows their stuff will be your true guide in the market.Secondly, I recommend asking those folks for good lenders, and also finding and connecting with other investors in the market (who have nothing to sell you). 

If this is true, I believe they will not appreciate with the SFR market at large, but rather appreciation will be limited by the ability to increase rent.

I have been wholesaling and flipping but ready to create true wealth for myself.  

That is true for maybe 1 percent or less of the wholesalers who try it.When you are new and you ask for a wholesale mentor online, you are going to get every pitch, course, guru sell that there is.