Zillow's API is no longer offered (or they make it extremely hard to access these days - have had no luck finding an updated link/page for it), Redfin has broad-stroke CSVs you can download that only give 5-10 fields of info and not often at the metro area, you can't legally create a tool to crawl these websites...I'm looking for 1 (or a handful of sources) to pull together basic metrics at the metro/city level for US real estate.

I think the question is probably too broad to answer. 

Broadly speaking, there are two types; offsite (like SFR, small apartments, etc) and onsite (large apartments with leasing offices on the property).For offsite, I usually see 8-10% of collected rents, half or all of late fees and 1/2 to all of the first month's rent. 

In the case of property, the value you get is measured more broadly than in dollars of bricks and mortar.

To make broad generalizations or assumptions about entire quadrants of the city being "problem areas" is an error in judgement, in my opinion.Now, there are areas on the west side that I definitely try to avoid, but if I have to go there, I make sure to do it in the morning hours when most of the delinquents are sleeping. 

Real estate industry is a ‘spectrum’ running from ACTIVE BUSINESS on one end to PASSIVE INVESTMENT on the other.

Investment Info:

Single-family residence fix & flip investment.

Purchase price: $900,000

Cash invested: $240,000

Sale price: $1,520,000

Was driving by home this time last year and saw a FSBO ...

I would pay them again in a heartbeat because of the added value of weather protection on the home.I would look into a couple more quotes to give you a broad range, which might make you feel more comfortable in whatever direction you go.  

If I tried to start today with the same funds I had back in 2018 I would probably own about 10 doors.In my opinion, it is really not a great time to be getting real estate (broadly speaking) - which when you think about it is the whole reason why the Fed cranked up rates - to slow down the economy, inflation, housing sales & price increases, etc.   

@Enrique HuertaIm pretty new so I started broad and narrowed down my search as I started to understand places a little more.