I want to ensure I include him on my list of contractors to monitor.

I also monitor new legislation.

Plenty you can do, even at 15.I think a guy your age for example could develop a nice small business of iphone consulting. 

Have you consulted a financial advisor?

Trying to figure out the optimal strategy that will provide liability protection, proper estate transfer at death, and other strategies that can benefit their tax situation.I have my ideas, but want to consult with someone who has estate and tax planning experience in CA.

It might be worth it to install some security cameras and signs saying the property is being monitored to deter criminals.

This is something to consult with an attorney about.

I’d recommend consulting with attorneys experienced in both Illinois and Wyoming laws to ensure everything is set up correctly.

I would recommend consulting with an attorney to find out why you would need a separate LLC for each property. 

I'm an Airbnb/VRBO owner myself, happy to help consult on some design improvements, but it'd be helpful to learn more of what your goals are.