Phone calls are not as effective as meeting and talking to someone face to face about what consequences they're asking for themselves.

Why ruin the tenant-landlord relationship over *paid rent*? 

The best approach to do it correctly is to systematize everything.And in that respect, it makes sense to use the same template.You can adjust that template as you go along.There is no point reinventing the wheel.Which is what effective flippers do. 

The best thing to do would be to start building relationships in the mean time like you said.

It appears looking from the outside he was the odd man out in the divorce so yes he will hold a grudge.Try fixing the relationship before forcing him to sell as most likely he would not sell in spite because of what happened

I have, however, a somewhat close relationship with the landlord I've rented from for the 8 years previous to buying my house, so somewhat familiar with the in's and out's and frustrations of rental properties.I'm just getting my toes wet and listening to YouTube videos, podcasts, reading content on the site, etc.

It shouldn't be a relationship where I find the houses I want and just use the realtor to sign the docs and collect a check. 

Listening to the BP podcasts, they are constantly urging you to create relationships with local banks.

Is there any relationship between the cap rate and the interest rate at all which will quickly tell me if the investment is cash flow positive?

Millennial's are a much larger demographic group then even the baby-boomers, and now they are getting better jobs, in relationships, getting married, having kids, and now moving to the suburbs.