A note on eligibility: your character will need to be at least 50 to hand in the items needed for King of the Fire Festival, and at least 65 to get the higher-level quests necessary for killing Lord Ahune in Slave Pens. With that said, we still recommend that lower-level characters participate, because you'll wind up with a ton of experience and gold even if you can't complete the meta-achievement.
Should you complete the meta, you will be awarded the "Flame Keeper" title. I've listed all of the required achievements in the order I think will be easiest/fastest for the average player to do.
UPDATE: Your character is currently unable to honor/desecrate any flame (including city flames) that you've honored/desecrated in 2008, which will make getting enough Burning Blossoms to purchase Midsummer clothing difficult, if not impossible. I'm still trying to find official confirmation that this is a bug (and I assume it has to be, as otherwise the meta-achievement isn't doable), but it also appears that fires have been added to Northrend as well. I'm heading ingame right now to assemble a list with coordinates and will update the post later.
Gallery: Midsummer Fire Festival 2008