You'll have to find ways to prove yourself as a real player because chances are they already have a rolodex of investors they go to. 

Who are the big players in the south side flipping and investing space?

Make sure you have your key players, cleaner/ restock person they will make or break your businessMaintenance person, things will break and they will need to be available.Sounds like a great place and best of luck to ya.

Again speaking from experience in the market I operate in only, Roofstock isn't working with ANY of the biggest players in the Property Management space only the smaller operations who have a bigger need for another company to funnel them clients as they don't have a robust enough business to keep their pipelines full organically.

Dollar General and Dollar Tree have been building ~1,000 stores each in the U.S. each year for over a decade, and I've read people on the forums who have pursued strategies for building and leasing specifically to these players at a high volume.How is this rate of new builds sustainable, and how can we determine the point of saturation, when the pipeline ends?

You can own Stocks with a top-tier brokerage, maybe JP Morgan or Vanguard, or even a newer player like M1 Finance.

As of late, some of the other big players have been trimming the fat.

Find those players, and after that "The rest in heavenly", or is there other things to be done before throwing the ball to the sky?

Wells Fargo is not an investor friendly bank, nor are any of the national players.  

You'll also want to get to know the players in your market; check out local meet ups and start to get to know people.