I like the thought of using lunar phase for it but since the moon is always full in-game (Correct me if I'm wrong) I think it's better to have a recurring date when it happens.
Sundays are the best day by far so my suggestion is to hold it on Sundays the week after Moonrise (first Sunday of the month). The main event should take place between 21-22 with possibility to continue for those who like to stay up late.
As for the event itself here are some thoughts
* In order to add some variation I think that the hunt should take place in a different location each time, like different parts of Ashenvale to start with so that every event is unique and can connect to the lore of the location.
* An introductory sermon is good, this helps build the feel and allow stragglers to arrive a bit late and not miss the action. I think we should start with retelling tales of the area we are going to enter to give a feel to the lands we visit. People should also be activated during the sermon in some way so they aren't chatting away in other channels and instead can contribute to the scene.
* The object of the sermon could be that one participant is selected, either beforehand or selected during the sermon by an elder. This person would be known as "The Stag" during the hunt and act as a sort of hunt leader like the dog for a fox hunting session that everyone follows.
* As the Stag rides ahead to the location of the hunt, the other participants follow closely wherever the Stag leads them, symbolizing the way Malorne knows the way for us all. (This may also symbolize the hunt for the White Stag as told by the Tauren)
* Upon arrival to the area we are performing the hunt in, the Stag selects a spot to stop in and all participants then surrond the Stag in a big circle. The circle symbolizes Elune watching over all of us and of her consort, Malorne, that the Stag represents.
* In the Circle the sermon is finished in some cool way, including all participants and the symbolic joining of Elune and Malorne to bless the lands. After this, the hunt begins for any animals or demons or whatever takes places either together as one group or through the whole area. Skinners skin everything they can and everyone loots everything they get a hold of.
* When an elder yells that the culling of corruption is enough. Everyone gathers and presents any good items found, leather and valuables and offers them to the Stag. This to represent our service to Malorne.
* The Stag passes the offerings to the Guild banker if there is one. From the leather, our leatherworkers should be able to make armour kits and other stuff for the guild.
...these are just a basic scenario. Feel free to add to it or suggest something else.