Looked into this in some depth back in NZ a few months ago (wanted to buy one as an investment). Can't speak for Sydney though, but some general advice ...
Generally speaking they're on lease hold land. You only own the building, and you should do a veeerryyyy thourough search of the fine print of the lease, with regard to things like your rights if they ever decide to expand the airport and build a new runway or terminal extension or car park in the middle of your hangar. Sometimes they're obliged to compensate you but a lot of the time they're not.
Obviously from an economic point of view, you don't get anywhere as much long term capital gain on a lease hold property, and most banks will only finance them to a maximum 50% LTV.
Talk to the airport manager about what you can and can't put into your hangar. There is a clause in most leases about 'aviation related purposes' only but they didn't seem to mind if you just store some stuff in there, in fact there was one bloke who had a car panel beating and painting workshop in one of his hangars next door to the one I was looking at, so I guess it can be done.
You can't 'legally' live in the things cos they're business premises, but everyone does it anyway, they just declare their hangar flat to be office / lunch room / toilet for the staff. The only big drawback, is that you almost certainly wouldn't get insurance if you burned the place down and they could prove you were living in it.