Also; he is planning on getting engaged to said girlfriend over the next year.

I would also add that the furnishing will have a direct effect on your returns.   

Since there are thousands of numbers, I want to be as efficient and effective as possible so I can go through many phone calls. 

I think it’s called form 1000https://guide.freddiemac.com/c...For example, if I’m purchasing a property where monthly PITI is $1,000 and monthly rental income is projected to be $1,100 does my “income” part of DTI go up by $100 and effective improve my DTI to qualify for the loan? 

If so, you can give the notice before the end of Nov and make it effective on February 1st, 2022.I always recommend giving proper advance notice and raising the rent on the Lease anniversary every year.

I wanted to check what effect the existing availability of homes will have on current multi-family rentals like the duplex in question.

Put $40k prepayment towards my current loan, effectively earning me 5.75% interest on the cash (penny saved is a penny earned).

I have been in real estate for effectively my whole life as an employee but am looking to build my own business/portfolio. 

First off, be careful of the influx of messages that will come in from all the sharks ;) There are actually other ways to achieve similar effects of a 1031 without having to jump through those hoops. 

How effective are those numbers now?