My biggest surprise on this last project was that they allowed standard 1/2" sheetrock for fire wall.

You could have a server or hardware firewall that does a better job of blocking torrents and providing security, but then you have to buy and maintain that.

Ceiling Sprinklers, Offices attached/detached from storage, fire walls or gap between buildings, Square footage per building before sprinklers are required.

Building code may be an issue, if your area requires a fire wall between living units, that means a fire resistant wall (block) that raises above the top plate about 18 inches I believe under roof, that would be hard to put into an existing building from the foundation up.By the time you do a conversion I'd say your tenant would be paying the cost of the add ons, you'll be paying for the house.

I learned that separation wall for a duplex could be a fire wall.

With the government storing so much information, hackers are constantly trying to break through firewalls. 

Bottom line, legal entities come in when your net worth becomes significant enough to create firewalls between individual pieces.Avoid large banks and google local banks and credit unions; with a decent credit score you will not have a problem to get a loan in your name on a cashflowing property.

AND, I would require that there be a smoke detector in the garage that is "connected" or "talks to" the smoke detectors in the house so that if a fire does break out in the garage, the tenants can get out out before the house burns down.I would also make sure that there is a sufficient fire wall between the garage and the rest of the house.

A better system would be for YOU to charge each applicant; you can still do it only but it provides you with a small firewall.

Together we can "fire" Wall Street and the leaches sucking us dry, telling us there "too big to fail" and how we must support there elitist existence so we can be allowed our pittance in return.