What Arney said ... it is really best to keep it outside.

Don't worry too much about the fuel's shelf life. I've used fuel that is approaching 10 years of age and it works fine and hasn't gummed up the stoves. The thing that damages most stoves I've seen is the gunk that splattered on the stove which can lead to rust. If you clean the stove with a soapy towel after each use it will last a long long time.

I would suspect the reason Coleman distinguishes between opened and unopened is that they cannot guarantee that a opened container has resealed correctly. My advice would be to protect the spout and lid after opening, and wipe off the spout with a towel before putting the cap back on. If it is treated well and not left open too long it should have the same shelf life as an unopened can.

I have never seen Coleman fuel in anything but gallon containers, so I can't comment on other sizes. Get the gallon container and don't worry too much. They are dirt cheap. They are reasonably easy to handle with a good funnel. I don't see much, if any, benefit to transferring the fuel to small aluminum containers if the seal on the original can is not damaged.

Do as suggested before. Buy a gallon of Coleman fuel, mark it clearly with the purchase date, and then use it directly from the original container. Though it is certainly not as safe as storing the fuel outdoors or in a detached building, I have stored my fuel in basements and attached garages for years with no incidents.

A Coleman stove running at full open is hotter than my propane range I have in my house, but not as hot as electric stoves I've had before. Its been a long time since I've used natural gas with a home range, so I can't comment on that.

Yes, you can leave the unused fuel in the stove. If the stove will remain unused for a long time (years) then I'd probably try to burn off the fuel to empty the tank. Have a weenie and corn boil or something to use up the fuel. Don't waste or risk contaminating fuel by pouring it back into the original container.

Having never used a kerosene stove, I'm curious how well they work. It seems that they'd stink a bit and that there might be a soot issue. Wasn't that the big advantage of the Coleman lanterns when compared to the kerosene lanterns??

One last thing: If you have the room to store a two-burner stove, then I would definitely suggest you go that route. They have lots of advantages over any one-burner stove. The lid and side screens act as wind blocks, which greatly improve fuel consumption and decrease cooking time - wind screens are usually recommended even with little backpacking stoves. The two-burner stove has a much bigger fuel tank, which means less fuel pouring and more consistent fuel pressure. Finally, the two-burner stoves have, well, two burners. Which means you can cook food on one burner while heating the coffee or wash water with the other. They are also MUCH more stable with large pans/pots - almost impossible to tip over, though I've actually seen one get knocked over in scouts - luckily it wasn't lit at the time.

Also, when lighting any stove make sure you light it VERY soon after turning on the fuel. I've seen many stoves blow or flare up become the dopey user turned on the fuel and THEN started looking for the matches. The same thing can happen on a home range or barbecue too though.