2) What’s the most efficient way to locate good Buy & Hold properties; utilize a realtor or simply use websites such as xome or auction.com?

Only problem is...not sure what’s the most efficient way of tracking them down.Buy a list?

It definitely can help to make the process as painless as possible and more efficient for both parties (landlord + tenant), and also offers digital leases.

I've seen formulas before $XX / unit, but I think there's a lot of variance based on locality, asset class, and efficiencies of scale.

If the landlord insulates, replaces windows, installs smart thermostats, and installs an energy efficient heating system the increase in value might well allow for a refi as long as the rents still support the new loan.

Very time efficient but not desirable.

Ultimately what an investor wants when a prospective deal hits their desk is the ability to analyze with efficiency and accuracy.

Caveat, I'm fortunate to have my rentals in an area where evictions, especially obvious ones, are a pretty simple and efficient process. 

Is it efficient monetarily enough to exclusively hire contractors to rehab the houses into rent ready conditions?

The biggest gotchas might be if the ceiling is low or the room(s) don't meet minimum size/geometry requirements,  the building requires a fire sprinkler system and that unit doesn't have one,  or if the city decides the unit must meet some kind of energy efficiency standards.