I’ve periodically had tenants at the Multis offer to “help with the landscaping” in exchange for a discount on their rent.

I wouldn't pay off the house entirely, as you can deploy that cash into more real estate or stocks.

Can anyone verify the tax treatment as of today that a gain from owner occupant unit is applicable for Sec 121 exclusion, and a gain from rental unit is applicable for 1031 exchange?

The benefits of selling as a portfolio is that when you do a 1031 exchange, you won't have to coordinate the sales of multiple properties, And this would minimize the amount of individual exchange fees. 

I don't remember what it was called or what it contained exactly but basically she admitted to trespassing and gave up all her tenant rights in exchange for $2500 which I sent via venmo immediatly after she signed.

This allows for a wide variety of ways to achieve the goal thru all aspects of real estate; investing in assets that have great capital gains potential but may not cash flow (options, land, redevelopment, gentrification, etc. ) utilizing “fee income” to build my estate (syndication, brokerage, partials, participations), and “creating” high yielding notes, and “creating” wealth through creative real estate buying, selling and exchanging. 

I've heard from several people who thought they had an owner finance agreement signed at the kitchen table, assumed they were paying down equity only to have the house sold right out from under them.Ben,  How common is this that a seller is willing to give up their deed upfront in exchange for seller financing.  

It was the same when I was actively involved as a day trader in the stock market.

I’m using funds from a 1031 exchange for the deposit.Can anyone provide insights or guide me on how to refine my underwriting or ask the right questions to ensure my numbers are accurate and this is a solid deal?

Almost all of the housing stock is 100+ years old so you're probably never going to see a home that is free of lead paint.