I live in FL, so no state income tax.

Do they plan on getting income? 

I would start by building out a basic P&L for what the property generates today vs. what it will generate in the future, and factor in any capital expenses required to get there.

Unless you threw them out, it appears they repaid your kindness by moving and generating a turnover. 

My current rent is $2300 at my apartment and I'm assuming the $2300-$2500 liability will be consistent in this property given the Purchase price, interest rate, and including rental income of $2000-$2200 of the other unit.

They always have capital outlay for months (sometimes many months) before any income (time value of money).  

Not sure if I’m kidding myself either  but I want additional income streams and I want them to grow over time.  

Your rentals should only perform better over time as rental income increases faster than property taxes, insurance and other expenses.How much will that contribute to your retirement income?

Simply plug in your Income, Expenses, and a few Cash Flow items and let the template do the rest.  

These plans are beautiful inventories of zoning, demographics, income, traffic patterns, etc. but now what?