I don't think there's any harm in your tenant knowing that you're a realtor if anything they would know that you know the law and won't try funny business.

Mold is in all the air we breathe it is just if it gets to dangerous levels where it could harm us. 

Which can harm the landlord.

What is the harm in waiting?

I doubt he will try to pass hurtful things as it would harm him as well. 

Some are harmful,  some are not.

Just a side note you need to understand the mortgage loan requirements and any house that was buying lt before 1978 or 1976 is subject to correcting and accessible to anybody for asbestos correction and that could be harmful for you.  

The main reason to set up an LLC is to protect your personal assets from harm in the event that you are sued. 

I highly recommend you partner with a experienced investor so you can learn how to do it properly from the beginning and don't leave yourself in a position that could cause you financial harm or damage your reputation. 

What you resent will not benefit you, it actually harms you.