You can use any weapon and any enchantment, but only defaults: no special weapons like Critbringer or Eventide. Remember, this is theoretical, so don't factor in cost or resources: there's no real limit here.

Depends: what type of damage are we talking about? (melee, ranged, magic, etc.)

Considering anything above 50 DPS is already OP, I don't know what to select...

20 DPS is OP for a beginner, since it kills most things in one second.

Pretty much.

This is too vague.

I literally said ANY WEAPON

"Considering anything above 50 DPS is already OP, I don't know what to select..."

Its really not... against powerful bosses, even 1000+ dps is weak. If youre still havin a hard time, look at it from a pvp perspective: enchanted diamond gear massively reduces damage, even in vanilla, and powerful boss monsters have similar amounts of resistance.