I find it helpful to have simple formulas for "back of the envelope" evaluations in finance (such as the 4% rule for retirement, rule of 72 for stock market returns, and car purchase price should be less than 1/2 your annual salary).

This forum has much -in depth- analysis of real estate (interest rate variability, etc) but I'm looking for some VERY BASIC things like:

(Assuming I bought a rental house for *CASH* (no loans/interest rates are involved)

-What is a formula should I use estimate annual expenses/insurance/repairs/taxes? (For example 1% of home price/value)?

-What is a formula for determining whether a rental house is a good deal? (for example, should monthly rent should be what percent of house purchase price?)

-Rule of thumb historical home value return (comparable to historical stock market returns)

I realize the any of these answers could be a book length, but I just want some basic formulas I can keep in my head.

Thanks!!!!