This is not an "Arms Length Transaction" and no banks that I know would lend you the money. 

There is no one-size-fits all rule about best investments.If you know rentals, flipping, or lending, then focus on that area you know best.There are considerations about keeping things at arm's length, choosing investments that are passive vs active in nature, and some tax complexity around the use of leverage that require some guidance from a professional but can still be very profitable.  

The first most important thing to understand is we are living in the Opinion-age, not information, 3/4 if not more of the people yapping on things are not actually involved in the first place, arm-chair-quarterbacks, it's a easy opinion of saying to wait from a person who was not doing anything in the first place. 

@Jason Arms for the info.

In general, what should I be reading, listening to, or subscribed to watch on Youtube so that I am armed with comprehensive multifamily knowledge, and plenty to speak about when an owner needs to be persuaded to sell at a better price?  

Jeanned D'Arc Credit Union in Lowell MA gave us a commercial loan at 3.5% on a 5/1 arm, amortized over 25 years with a 20% Downpayment requirement.

@Troy EvansOne of our management companies does a semi-annual "fire safety" walk through.

I should probably add, my wife (who runs most of the projects) would be handling this arm of the business.

We used an asset based (aka "hard money") lender as we don't have W-2 "income" and my husband is our strong credit arm. 

If you go to the Dr, with your arm hanging at your side, and when the Dr asks you what's wrong you tell him it hurts when you raise your arm.