[ewill3rd]

I don't think that tank has an anti-siphon valve in it, if you think it has that much gas, try to get some out.
You'll need to lower it on the left and slide it out, with the fill hoses disconnected you might end up taking a bath.
Lower the heat shield. There should be several 7mm fasteners holding it to the body, just the rear portion needs to come loose, you need not remove it, just lower it.
I use a swivel socket to get to that front bolt.
Raising the car up as high as you can is good, use jackstands to be safe if you have them.
If the rust is so bad the paint is bubbling off and you think you could punch a hole in the filler neck now might be a good time to look for one. Some rusting is normal and unless the metal is just crumbling you might let it go for now.
The lines are attached to the pump on top, the best way to do it is to disconnect the pressure and return lines near the filter, then find and disconnect the EVAP canister hoses, drop the tank with the lines attached but be sure they are disconnected from the lines on the vehicle.

The procedure on replacing the filler neck usually isn't a big deal but on your specific vehicle I don't think I have ever changed one so I can't offer you much in the way of advice.