The Avari faction would be very interesting. I am thinking for this that it would use the single mod lore-text we have on the Avari as a main reference.
Avarin Steel Ingot: Smelted from a wood log and an iron ingot/ore in a Dwarven Forge
Avarin Steel Block: Nine Avarin Steel Ingots in an Avarin Crafting Table
Avarin Crafting Table: Four planks in an Avarin Crafting Table
Avarin Armour: Armor Recipes, with Avarin Steel
Avarin Tools: Tool Recipes, Avarin Steel
Avarin Weapons: Weapon Recipes, Avarin Steel
Avarin Steel would be a gray-ish colour and the armour would be gray-ish, but would have the 'green and purple' described by the mod lore text. Unlike other elves, the Avari would have a hammer due to their close proximity to the Dwarves, yet would also have a battlestaff.
Avarin Alignment would be centralized around the Wildwood, and a new Wildwood biome would be created so that Avarin structures and npcs spawn just there. The Wildwood would most likely have bigger trees than a normal Rhun forest, more similar to Fangorn.
Avarin structures would be hidden in the treetops and underground. The Avari would spawn at night, never at day. They are not inhibited by the sunlight, however.