Yes, the spout is small enough to fit a car or trucks gas filler tube. I filled my portable generator's fuel tank with room to spare, and poured the left over fuel into my pickup with out the need of a funnel.
Yes this does not leak fumes BUT for long term storage, go to your local boat marina and get ethanol free Regular gas. The crappy ethanol gas is harmful to boat motors and if the truth be told, bad for your car engine too. When FLorida required 10% Ethanol gas in 2012, my Jeep lost 4 miles per gallon. I use Marvel Mystery Oil to negate the Ethanol and got the 4 MPG back.
Absolutely. If you are concerned about the temperature inside your shed, it may be stifling in there, but it's out of DIRECT sunlight. And as long as it is ABLE TO BE VENTED. Vented being just by opening the door(s) or window. You should have no issues at all storing this style fuel container in a plastic shed. If you're concerned about temperature differences, get one of many different types of Laser Temperature gauges to check the difference in temps to find an optimal location to place your can. Also, all these "New Design" gas containers have a way to vent them before use. One thing that I picked up from my 20 plus years in the Army is to use a metal cabinet for Hazardous Materials. So I purchased one of the metal cabinets from one of the big box stores, I store my 2 small gas cans (1.25 gal) of 40:1 & 50:1 mixed for different motors, paints, poisons, ground clear, and anything else that needs to be all in one spot in case of emergency. This will give you a second layer of insulation for your fuel can as well, but make sure you can vent this locker! My 5 gallon gas and diesel cans are kept in different places, but as long as they are kept out of direct sunlight and are in an area that can be vented, or is well ventilated, I have no issues.
If you buy it in the store, Yes. If you have to order it online, No.