It depends on where you are. In most U.S. states, you can legally shoot a firearm at a shooting range, or outside the city limits in some counties.
No. You can go to a gun range and shoot.
Some are rimfire, some are centerfire. Depends on the design of the firearm.
hungover
Not unless you were unlawfully in possession of a firearm that you shouldn't be.
Ready to shoot
No. However, local ordinances may prevent you from being able to discharge a firearm within town limits and such.
yes
ANY mechanical system- including the safety on a firearm- CAN fail. This is the reason for the basic firearm safety rules- including "do not point a firearm at anything you do not mean to shoot." It is rare, but CAN happen.
Any firearm chambered for 22
DO NOT ATTEMPT TO DO THIS!! Never use ammunition in a firearm not designed for it.
That varies by state but generally you must be off the road right-of-way and you may not shoot across the road.
If it is BB or a pellet gun, yes. A real firearm, no.