Upgrades such as security gate, cameras, 7 renovated units, Hvac units.

It would be cool to mount project cameras that create a time lapse of each process.

Having had one done recently with a camera inspection on the main line, the inspecting plumber noted that the pipe had tree roots on several parts of the mainline.

You should upgrade your properties to be monitored remotely with software, apps, wifi, thermostats, locks and cameras. 

I'd set up a camera system and a DVR.

A few more things, always get a permit, have excellent insurance, set up security systems with cameras right away and really pay attention to your carrying costs.

When you have roots present, you need to confirm with a sewer inspection (camera) that those roots are just sliding in through the joists and that there are no breaks in the sewer line.

Have a plumber come in and use a camera to inspect the lines.

He is also very suspicious... parks very large vans (about 4 to 6 at a time) in front of his property and on his driveway to cover the house, has cameras everywhere, is hanging cloths from his patio cover so no one can see the inside of the house, etc. 

You can also put up a sign saying the areas is under surveillance should the talk with the neighbour and a copy of the lot dimensions not work.