Benders are not invincible, so a fire arm could kill them. But it depends on how fast you are, they might get to you first.

I agree with @Jynxco if they don't deflect the bullet, then yes.

Benders are still human. However, a metal bender may be able to bend it away depending on the material of the bullet.

Yes. @KayakNinja07 you phrased that perfectly.