I will be closing on my first two family house so I am relatively new in the land lording business. 

By the way, I use property radar to look for this data. 

After analyzing properties you should get a good feel for what is possible, and what is a good deal in your market (it's all relative)

I would calculate a percentage from existing listings using sales data and the appraiser's website.

That's really what cryptocurrency is all about; highly encrypted data that has innate (or at least agreed-upon) value.

My business partner and co-trainer in direct marketing in GaREIA the largest local group of investors in Atl/GA uses;- Equitydepot.com best source, more expensive, just gives you a spreadsheet but all the data about the house- realtytrac.com cheapest but comparison finds it has not all the pre foreclosures per county each month. 

For example, I lived on plum street which is relatively deep for college kids (cheaper rent), and we had drug dealers 2 houses down, college kids next door the other direction, and hard working Hispanic group near one corner.

Of course depreciation on those properties would be relatively worthless to you, but run the numbers and if it benefits you more to have new investments in your retirement accounts you should pursue that.

Each time you create a new LLC you will need to file documents with the state which have filing fees and will need new operating agreements and related documents. 

There are additional rules relating to this, but that is the gist of it.