Just for giggles I did some quick math to determine 2012 expense ratios (Expenses/Gross Income) for a couple of my properties for which I have the data handy.4-Unit: 52%SFH: 35%2-Unit: 78%2-Unit: 34%2-Unit: 28%Sort of a scatter-shot...and it will be different in 2013 as new maintenance and repairs are done on some units, and other units require less upkeep as compared to this year.My experience (and I'm by no means the most experienced REI) is that the 50% rule is pretty close for my portfolio.

However, one year actual data is all I have for my properties since I have only started investing recently (late 2011).

@Mike D. there are a number of sources for rent data.

Here are a few of the issues that go along with the change:- We currently have all of our data on an SQL server and will need to get it transferred if we go to a cloud-based solution. - Many employees at the company have been here 30+ years and are not fond of change or new technology.- We have many Crystal Reports that we had custom made to the boss's specifications.

I can attach a screenshot with personal data blurred out, but here's an example of the text I see:Member Number Creditor Status Narratives COLLECTION / COLLECTION Collection account Account information disputed by consumer and then the next column:Industry Code Account Number Collection Services 35803973001Beyond that, it's just the dollar amount of what is owed and the dates related to when the account went to collections, the last update, and when it was closed (no entry for that). 

Do you know of any data available to make an educated guess on the kind of vacancy rate I should expect from a 4 bdrm home in West Nashville.

I hope it is helpful. http://www.esri.com/data/esri_data/ziptapestry

What makes them fun is going through the exercise and come up with your prediction that is backed historical data or your own theory. 

Real Estate (Buyer's) Agent: This is the person who can provide you the data to analyze your market (to determine if you actually want to invest there), can provide you local expertise and who can provide you access to any properties listed on the MLS.2.

The appraisal is an OPINION of value derived by analysis of the market data.