So, as far as I can tell the event is play event levels, receive items that you trade.
The first set of maps, available from the 18th give you items that can be traded for fire and earth levelling and maybe evolution items

The second, available from the 20th give you items that can be traded for wind and water items

The third, from the 22nd give you light and dark

Throughout all of this you can get gifts too, which can be traded for Sonya (maybe only from the start of the third set of maps?), medals, and gold evolution statues. Also for gold present boxes.

The gold present boxes can be traded for 5* limit break material that is dependent on show, not class. The shows available are urara, kiniro, A-channel and new game. You can only trade 2 of these, though I'm not sure if its 2 for each show, or 2 in total.

It's should all be fairly obvious once the event starts, but at least they do seem to be giving out 5* limit break materials in events.

All of the worthwhile stuff seems to be limited to presents, and it doesn't look like you'll be able to exchange the other items for presents.

**Try getting Sonya and the limit break items at least if you are unable to play the event as much as possible.**

Update: 20 stam run on the event is the most efficient thing for leveling rank and kirara right now. Also for collecting event materials it seems since its 3 rounds of 3 enemies each

There are 2 more "seasons" to go. they're probably gonna be similar but with the other christmas drops instead of wreaths, but it would be smart to wait to use your watches (AP refillers) just in case the rewards become better in the newer seasons for everything, unless you are unable to play the game in the upcoming start of the week given the holidays.

To complete this event you'll neeed:
1600 wreathes
2520 baubles
1600 candy canes
3000 red gifts
2 golden gifts