I would never use CO2 as a propellant in an area where I am sitting and painting. At my company, we sell fire suppression systems. CO2 is a great agent for fire suppression, it is also a great agent for depleting oxygen (that's why it puts out fires so well) and, as pointed out in another post, it is a greenhouse gas. One suppression agent we sell is called Inergen. It is a combination of Argon, Nitrogen and 8% CO2. Some of our customers refuse to buy anything that contains CO2, including Inergen. Some jurisdictions require provide that CO2 can only be used where there is no alternate agent available.
I'm not suggesting you'll suffer horrible consequences from exposure to CO2 in the small amounts used while painting. I am saying, however, that we tell our customers who use CO2 to evacuate an area that has a CO2 discharge. (If you insist on using the stuff, make sure that you do so in a well ventilated area that is exchanging large amounts of air - and that you're using a spray booth.)
My opinion... buy a silent air compressor. If a landlord has a problem with a compressor, I'm sure he'll be happier with that than knowing the pressure that a CO2 tank (or any compressed gas cylinder you have to buy) typically contains. As for the cost, by the time you buy a storage tank, a couple of regulators, hose, etc., You could buy a very nice compressor - even a pretty silent one. Besides, youll probably end up buying a reserve tank after you run out of CO2 some Saturday night right in the middle of a airbrush full of paint.
Wait until your fill station refuses to fill your tank because it's now due for hydro-testing. (if they want to keep their DOT certification, it will happen).
Just my thoughts on the subject. Hear me now, believe me later.