After purchasing the handsets, I can change the cylinders in about a minute each.  

Question - Should I keep the original Unit 2 entry in the enclosed hallway (would add double cylinder lock to the door)? 

We were lucky enough to have enough to supply downpayments to get the ball rolling but since then have bought 13 buildings, totaling 51 units and have since sold 2 SFH and now have 48 that are running on all cylinders and providing enough income for our family of 3.

On my rental, I have locks that have a removable cylinder. 

Your staff will make or break you.I've learned how important it is to have a great manager and a great nurse on staff - we had only 50% of that for quite a while and no matter how great the other part of the team is - if you dont hit on all cylinders it makes it hard.  

The plastic handles would strip from the shutoff cylinders as the corrosion was excessive & the water dripped constantly, those high water bills would eventually pay for a new bathroom.

However, the CAD economy is firing on all cylinders at the moment and real estate prices are analogous to US prices circa 2006-07. 

You can change out lock cylinders and just have a few extra and rotate among properties.

https://www.lowes.com/pd/Kwikset-SmartCode-SmartKey-Venetian-Bronze-Single-Cylinder-Motorized-Electronic-Entry-Door-Deadbolt-with-Keypad/50281629?

I will say they are even more responsive now than a year ago and their systems are really firing on all cylinders I feel like.