Apartments as investments

I have been hearing a lot from the Gurus about buying rental properties as one of the best ways to gain long-term wealth. I am very interested, but was wondering a few things. I found one apartment building listed with 18 units. It states that 2 are 1 bedroom and the other 16 are EFF. What is EFF? I found one place online that said it was an EFFiciency unit, but what does that mean? Is it like a studio?

Has anyone purchased both apartments and houses for rent? What are pros/cons of one over the other.
And finally, does anyone have a document that they would like to share that they use to calculate cash flow? I just want to make sure that if I go this route, I'm not forgetting any expenses. i.e.

Gross Monthly Rent: $2,000
Tax: $100
Mortgage: $700.
Etc..
Net Cash Flow: ?????

Thanks