The level of the quest you are offered is random (30, 32 or 34).
Lower level characters may not be offered the higher level versions (needs verification and specifics).
You may delete the quest and re-acquire it if you like without any penalty.
Completing the required kills immediately completes the quest, and Master Eldin Necrosis immediately offers it again.
Only the level 34 version rewards armor.
The level 34 quest reward is listed as "You will receive a piece of Ravenring armor", but you also receive an unlisted coin reward. Therefore the actual minimum amount of coin is an estimate; no amounts less than the value shown have been recorded.
Most of the monsters required for this quest do not respawn, but none trigger the zone's lockout timer, so you can leave and re-enter to respawn more.
Leaving the zone does not immediately respawn the Lesser mimics, they seem to be on a timer. As there are only 3, you have to wait out the timer twice. It is advisable to delete and re-acquire the quest if offered the Lesser mimics.