I understand that this will necessitate working with property managers, but I am hoping that I can build a good team for mutual benefit.  

Two of our purchases depreciated close to 20% after purchase (and both were purchased at retail), but both are up over $1K/month over the hold period now (1993 3/2/2 SFH purchase in Claremont for $167K, worth ~$700K today; 2003 4/3/3 SFH purchased for $741K, worth ~1.25M today).OOS almost necessitates use of a PM. 

You may not plan to, but what if something happened in your life that necessitated that you sell? 

Both are basically "selling stuff" but the difference in magnitude necessitates different skill sets and network. 

I was also thinking about long-term for example I see pre-war homes on the market, and if you are a buy and hold investor you might be owning that asset for another 10-20 years, which in theory necessitates a remodel at some point in the future..

Coastal stuff built in the 1960s had none of the earthquake and geotechnical requirements we have today, and parts of the coastal areas present challenges (I'm doing a project about 4 blocks from the water now that happens to be in a liquifaction zone, necessitating plenty of soils work, even for a small addition).I guess my only other comment is the use of the "construction crew" ... that's no small feat at the moment. 

I looked at the property records - expansion would be possible but would necessitate the purchase of an adjoining property.

You may be much better off having a consultation with a local real estate lawyer before you take action on your own that may necessitate quiet title procedures on both properties later.

We are wanting to increase the number of concurrent projects which necessitates using GCs in addition to our own crews.

It's a clue and reason to be on your list of targets.However, as David mentions, most are paid (late) without necessitating a sale.Now, if you combine your tax list with other triggers such as foreclosure and probate, etc. you can build some pretty incredible motivated Sellers.