We built out a Diligence tool that grabs data from multiple sources ( Paid and non-paid), aggregated together to give us data on multiple properties in that matter of minutes. 

So it's more so a data aggregation tool that allows you to even download all the data of all the listings with 50 miles of the city that you're targeting, cities are limited as of now.Though it would be cool to do something like that, it's not the intent.

Many of the best longer term markets are in a correction now (TX/FL).There is no particular formula, but the closest proxy would be population growth and 10Yr historical price increase which aggregates many factors together.

Such projects can also be found in New York upper states or states with community solar aggregate policy.

Whether you do that or not I don't think that will solve your problem (and I would generally recommend against it if it's a decent property as lots of Section 8 units together concentrates poverty and can bring a property down; yes there are plenty of good Section 8 tenants but we're speaking in aggregates here).The big thing you need to do is find a way to get all of the problem tenants out.

I exported it to a SS from Steassa, added columns for the dep lifetime and dep already taken, and went from there.Getting it back into QB wasn't that difficult, since it's just the aggregate.

Also, do the aggregate losses above any W2 income get carried over to the following year?

I am reading through the "Real Estate by the Numbers" book now, and am still in the beginning where it discusses personal financial statements.For the past two decades I have been using financial aggregators to monitor my finances.

Can the top aggregate be sold.  

It's like the Zillow Estimates... it just aggregates the data from across the board, which is a good start, but it won't account for nuance and detail (e.g. a corner property selling for a 5% premium compared to non-corner).