I'd like to set up something that gives us an alert if someone is at a vacant property after-hours and to determine if a home is occupied without paying someone an hour round trip to find out (for the rare default situations).  

In order to facilitate a 1033 you would sImply use those funds to either rebuild on the land, or the replacement can be a new investment propert purchase.

I guess I need help determining how to locate properties to be able to crunch the numbers. 

I'd encourage you personally to either consider a strategy that allows you to add value quickly and get out quickly (a Flip or BRRRR) if the HELOC is your current only/best option for cash, and/or to simply save up.

I simply call my broker and add the customers name to my liability policy.

If you do not close on enough of your properties to defer all tax you will simply pay the same tax you would have at the same time you would have.

Don't give names or addresses, but simply ask hypothetically. 

Yes don't split it as that is making a determination that they are owed it equally.

Seems to me whatever % you would give up would be offset by simply renting out the upstairs unit.    

I’ve heard from some investors that are perfectly okay with simply breaking even on rental properties in the current market, but I’ve never had the risk tolerance for that.