Rental Property Investment analysis

[Mike Henson]

I am just beginning my research into investing in rental properties as a way to augment  retirement income and have a few (hopefully) simple questions as follows:

1. Generally, when stating a "per door" income, what are you deducting from the rent to come up with this number?

2. The "2% Rule" says that per month rent should be equal to 2% of the sale price.  Is this legitimately attainable or an exception to the norm?  When I find a property that meets that criteria it is almost always in a (fairly) depressed area.  However, I wonder if a property meets the 2% rule, is it always (or almost always) a good investment given the goal of passive income?

3. Are capitalization rates subjective assessments or pure math (NOI/sale price)? Should the cap rate be a part of my analysis and if so, how is the best way to think about it in my market in metro-St. Louis, in Madison County Illinois?

Any help is greatly appreciated.  Thanks in advance!

Mike