@Greg Brake Hey Greg, Welcome to the site.

Banks have a way of putting your brakes on for you, don't you agree?

So my fuel or energy to move the car is free. and there are no oil changes or tune ups.. just tires.. and with the regen braking you hardly use the breaks.. its really a genius car and totally the right machine I think for running folks around...

The only thing that would stop it is if there was a big expense (because that's where my dad would be more likely to put on the brakes).

Three.......refer to number two....whether it's regular wear and tear...when it brakes....guess who gets to pay for it.

At my "normal" job I am the engineering Director at a large automotive aftermarket company managing approx. 85 employees, budgets, strategic planning, etc., etc. 

Should I put the brakes on trying to set this space up as an additional unit? 

There will likely be significant traffic noise, including big trucks using jake (engine) brakes to slow down. 

Even if there were an aftermarket product to convert traditionally vented (i.e., vertical) water heaters to direct vent, it's likely to void any warranty and create a potential liability.  

I just added one item to my checkllist for when a tenant moves out - Turn off the water valves to the toilets as I just (for the very first time after all these years) had a toilet brake and cause moderate water damage to my rental home.