Remind him to buy the properties in an LLC.

Buying one, fixing it enough to rent, then renting is a pain in the ass.
It is why the big firms didn't invest in small realestate until lately.

But, if he does get the hang of it while we are at the top, he will know what to do when the crash comes... if he still has any money. (also the reason for the LLC. You can basically give it all back to the bank)