Trulia provides a crime heat map with a few details on the type of crime, as well as general information on schools, commute, demographics, etc. 

If you're not on the MLS, you'll be missing the largest demographic of potential buyers.Now, you can list flat fee on the MLS, but I don't like that route either -- many buyer's agents will steer their clients away from flat fee listings, as they know that dealing with flat fee sellers is more difficult (there isn't much support on the listing agent side).I've sold hundreds of houses, and I can only think of a very small handful where the buyer lead came from somewhere other than the MLS or a buyer agent.

- Where is the best place to get demographic trend info?

It could have much to do with "certain people" part of the formula, but, I also determined that my target demographic starts their apartment search on Facebook, and so some percentage of my customers never get to my listing on Zillow or Craigslist because they started the search on Facebook marketplave and if they found something there,they never even got to the places where I actively advertise.

Though I will disinfect surfaces that I touch, home sellers are encouraged to clean or hire a cleaning service after the inspection, especially if they are in a high-risk demographic.

I work mainly with lower income demographics, so I utilize Facebook most of all.

You might have some success there, but as others have noted, you have to account for demographic shifts in your vacancy numbers. 

Be sure to have the following as a starting point: detailed property information, analysis of the property numbers, demographic/population trends, supporting rent comps, clear investment structure, financing/cap ex costs, and a business plan.

You would filter by certain demographics and property conditions, then download a list of properties that fit that criteria.

IMO most important high level metrics (without getting into the weeds/complication of projecting demographic shifts, etc etc) are pretty straightforward: 1) Payback period (actual cash in in upon refi within ~6 mo or so, if a value add investment, divided by stabilized cash flow. or if not value add, then down payment divided by cash flow).