Treebeard is an amazing hero, his ability to be a powerful quest and attacker is quite unique; however, there're a few things that get in his way, such as the need for readying, and the need for healing.
Legolas is a card that I hold very dear(the Harad box was one of my first expansions) and his ability to constantly ready another hero can be really powerful if used well. Treebeard can really appreciate having access to such an ability, this way we get a lot of flexibility in how much we can quest.
Having such an early potential for questing power, allows us to go for this first sub-theme idea: Sidequest. Then, it becomes a no-brainer to choose Thurindir as the last hero in the line-up. The first quest we should be going for is The Storm Comes, which allows for a smoothen our curve and opens many possibilities in the allies department.
We'll have a bit of a bottleneck on our Spirit resources because we need to keep playing Elven-light in order to fuel Legolas' triggered ability and Song of Healing(another key piece for Treebeard). Luckily, when we complete The Storm Comes, we can start using our two Lore heroes to pay for our key spirit allies, like Rider of Rohan and Glorfindel.