If you're doing the work yourself and don't mind extra work, consider pocket door or barn style when space is available.

Location is the biggest but maybe it's a standout from others in a similar price due to size or style, etc.

You need written guidelines but they should be drafted with flexibility so that the landlord can make reasonable choices, income at 3 times the rent is a good threshold, but even that becomes irrelevant at lower and higher income levels, what needs to be examined is the cost of living and disposable income as well as the life style, are they young folks who may want to go out or is it a 72 year old lady who stays home?

I posted an ad on CL and found one for $50/hr and one for $65/hour and they both have more than paid for themselves in the deals they've been able to find on furnishings as well as the style that they bring.

Type/style of property is not as big of a factor as location and cosmetics. 

Awesome achievement!

I have family members who have been able to successfully leverage real estate to achieve financial freedom and seeing how they are able to live gives me something to work towards.

What do we want to achieve? 

USPS has added street address style option for their P.O Box.

I focused on my IT career and advanced it pretty far but I'm not going to achieve financial freedom or retirement with it.