Potentially negotiate better rates with different trades due to our volume- Work on larger capital projects at some units, as well as strategy on remodeling units such as certain types of materials, etc- Help network/find/analyze potential acquisitions- Manage rehabs of properties that are recently acquired before they're put into service- Produce reports on performance of properties that can be shared with future investorsHave any of you out there hit this stage that could provide some guidance on how you have continued growing once you've hit this stage?

However, the consistently rising prices and limited supply actually led to year-over-year declines for June 2018 in median prices, number of sales, new & active listings, and total dollar sales volume. 

TM Neil Henderson - 2018Never Eat Alone, Expanded and Updated: And Other Secrets to Success, One Relationship at a Time by Keith FerrazziBest Real Estate Investing Advice Ever, Volume 1 by @Joe Fairless and Theo Hicks...and I second the recommendation from @Alina Trigub on David Lindahl's book and @Spencer Hilligoss recommendation of Crushing It in Apartments. 

That would be super helpful in hypothesizing what the next high volume neighborhood will be. 

Is data on metrics like sales volume, or $/sq ft, by month and year readily available?

The volume of sales is still way off the peak in 1999, and the peak price in 2006. 

If getting up into some serious volume, an s-corp tax designation can help with some SE tax relief.  

Forget the books, get some real experience working at a call center pushing out large volumes of loan business, you'll learn more in a couple of years doing that than you will reading books.  

There's  volumes written one the subject  here in Bigger BiggerPockets.

That speaks volumes about you.Good luck .