I guess that you can make a Range Attack against a Zombie in the same square (point blank) as long as you don't use the weapon more than once?
Also, can you fire at a distant Zombie with Ranged Attack if there is also a Zombie in your square?
The range is the maximum. You can still fire into your own space. In fact, it's often a good tactic if you're the only one with decent weapons: enter a space, fire at one in that space, melee out the rest.
And there's no problem at all firing to zombies in other spaces (as long as they are within range) if you're in a space with zombies.
This is all correct. In fact, I believe I read in the instruction manual from the basic game box that you can fire your ranged weapon at a zombie in the same space as you. That's part of your arsenal of tools...use it!
Also, while shooting the zombie in your own square usually makes sense, heroes are free to shoot a more distant Zombie instead, if they choose to. There is no "Zombie hunger" equivalent for heroes, so the heroes can always make the choices they think are strategically best.
Has anyone tried the house rule of -1 on the die roll needed to hit if firing Revolver or Shotgun at point blank i.e. same square? Out of ammo roll of 1 or re-roll still apply.
I wouldn't change the die roll needed to hit for a rifle as that's quite hard to aim and use at point blank / in a struggle.