Do seeds work on survival mode in Minecraft?

Yes they do, just remember though, seeds can change after updates so make sure the seed you want to get is for your Minecraft version.

Yes.

Yes seeds work, but every update changes world gen just a little so if you want the same seed as someone else you have to be using the same version of Minecraft.

That includes having the same version of the same mods as well, as many mods alter world generation.