So without putting a sub panel just clamp the clamps over which breakers go to the separate living area (If that possible) and track total KWs usage and bill that to the tenants.

You likely need to limit hours of usage and perhaps have specified quiet hours so everyone can sleep.

little do they realize how much it can cost.Anyways i am starting to look into smart water metering so i can divide the quarterly bill and allocate it towards their water usage. 

What documents do I need from the seller to verify the current usage is grandfathered in and in conforming status?

But if everyone denies it and the water bill goes up do to usage, then everyone will receive a rent increase. 

He said "I didn't know that".After the contract signing, several people in the room commented to me that they thought it was inappropriate.

If not, then the airbnb usage is not sustainable and the highest and best use is for rental.

Emotions are a sign of weakness and inappropriate in business.

So there is the conundrum; does my usage of that $50k beat stock market returns?

in California as of 2020 it's not legal to turn anyone down because of section 8 usage but you still can have tenant requirements like good credit or minimum credit score that you follow for everyone that the section 8 tenant likely won't meet.I waived those for the section 8 tenants that I mentioned above and thankfully it worked out but when I had done so for other tenants not on assistance it has bitten me on the butt.Long story short: if you screen section 8 tenants like you screen your other tenants (with a little wiggle room for their financial situation), interview them/their current landlord (if you can), and you don't mind more government intrusion into your business (property), then try it as a one-off to see if you're okay with the level of administration required.