You are comparing apples and oranges. You don't have a SRW with real estate. With stock/bond investments, the increments of money are small enough that you could liquidate roughly 4% a year. With 4 properties, your option would be to liquidate 25% of your holdings at a time.
RE is special in that you buy it heavily leveraged (mortgage), you have someone else pay for the mortgage (rental), and assuming you bought it right (low price, good rate, well managed) then you can get much higher rates of return than passive stocks. Also, depending on how big you build your portfolio, you have a built in retirement job (landlording) which some people enjoy and others HATE. You only know after doing it a while. Most end up hating it. Like anything in life, YMMV.
I'd recommend a path of diversifying in both stocks and RE. I max out my Roth IRA and my Simple IRA as well as my wife's so we save about $37k a year into stocks. The rest of the savings goes toward RE purchases. I would not put all your retirement eggs in one building or properties in one area. Diversify.
As far as your calculations go, RE historically appreciates at the rate of inflation ON AVERAGE. It may go up or down wildly in any given year though. So for your modelling, you can assume that rent increase and appreciation will be at 3%. Assume vacancy of MINIMUM 5%, 10% to be more conservative. Number 1 rookie mistake is to model out unrealistic expectations and results and then get hurt if you can't meet the 98% occupancy you need to pay your mortgage.