Questions about factoring real estate holdings into FI planning

[Eli Altman]

Doing FI (financial independence) math is simple when you're only invested in stocks/bonds. Knowing your savings rate, and expenses + using tools like Networthify/FIREcalc get you there pretty quickly. MMM talks about how easy it is, and also says the real estate can be a part of a FI plan. I just haven't found any specific guidance for how to incorporate RE into the calculations.

Should I be basing it off net income? Equity? Both? Equity isn't accessible in the same way it is with ETFs – buying and selling is a much more involved process. Net income isn't stable to the point of being able to count on a specific withdraw rate. 

So what's the best way to think about real estate holdings as a part of a FI plan?