Yes, there will be similar restrictions like the Challenge events (Maximum 3 star heroes, 2 star troops and battle items for rare, etc…) , and there will be 3 tiers, and you need to completed them starting from Rare to Legendary.
So you can not choose to complete just Legendary.
You can not start Legendary before finishing Rare and Epic tier.
I am now working on update the event texts, and updating the rewards sections.
(Some data is still not fully collected for that).
Sneak Peak: Ice Aethers will be included in the loot other than these new Master Trainers:
In general more loot will be given after all levels.
Update
I have now updated the OP with these information.
I am still working on the Rewards section.