Cash flow after mortgage...

[Anna Markowski]

I'm a newbie so I might be missing something, but I'm not quite sure why no one ever talks about the cash flow they will have after their mortgage is paid off. I currently work in the non-profit world and just bought my first 4 flat; I'm house hacking. We live in a neighborhood that is rapidly gentrifying, but we believe in keeping our units affordable. Even while doing this we pay very little each month out of pocket, about a 1/4 of what we would renting the 2,000sqft space we have to live in. Our plan is to be able to raise our family in this home, and eventually, take some money out to buy a few more 3-4 unit buildings. Our goal is to be able to do the type of work we care about while still securing a comfortable life for our family and healthy retirement plan. So, as I think about this, especially as it comes to retirement dollars, I'm not sure if there is something I'm missing. On the BP podcasts Brandon talks a lot about cash flowing $200/unit per month, taking half of that for retirement planning, and then multiplying that to get to your goal of income per month. That makes sense to me if I'm thinking about quitting my job today. But if I'm thinking about this as a retirement plan the numbers are very different, no? For my current building the rent, minus my unit would be 4K/month (not including expenses (which won't be much one the mortgage is paid off) or the inflation in 20-30 years). So that's $48,000/year - expenses & taxes (at this point depreciation would likely be exhausted). I just want to make sure I'm doing the math right and that I'm not missing something. Everyone on here seems to talk so much about the short game that I can't tell if I'm missing something and that my math is for some reason way off or if I'm just playing at a different game than others. Would appreciate your thoughts. 

Thanks!

-Anna