First off, seeing as this is your first post to FSM, welcome to the forums.
OK … now for your questions
Not really … you’ll go through 1 or 2 cans per model anyway. A compressor will supply you with a constant and controlled flow of air where as the cans don’t.
Depending on where you live (Canada, U.S., somewhere else). You can pick up a single action Paasche Airbrush for $69 in some locations in the U.S. Add to that a compressor from Wal-Mart or any good hardware store for between $99 and $129. By using a small industrial compressor you have the option of more uses around the house while a hobby compressor is pretty much limited in it’s usage. Final things to make sure you have are a regulator (which sometimes comes with an industrial compressor) and a moisture trap (very important and costs about $10).
Depends on what you want to paint. I only use a single action airbrush for painting my armour kits. I can achieve the camo looks that I want to do so I really haven’t found a need for a dual action unit yet. Also the learning curve with a single action is much smaller.
I went to home depot and picked up an air tank (5 gallons) and a regulator, total cost: about 40 bucks. My schedule for completion of kits is the same as you, I find that the tank holds enough air to complete 1 - 1/48 scale airplane. when it is empty I just fill it up at the station.
My airbrush is… forgive me, an aztek It works well enough if you take care of it, and their customer support is excellent, my A320 went kaput so I sent it back and they replaced it, no questions asked. hope this will help
Check eBay. There are always airbrushes and compressors out there - some for way cheap. I have seen ab / comp sets go for less than $50, if you dont mind a used set up.