Stormheim is the zone you want to start it. For some reason Legion treasures are not worth any experience like they are in WoD...except in Stormheim. I haven't been able to find out any reason for this, and it's possible it may get fixed/nerfed at a later date. But for the time being you REALLY want to jump from treasure to treasure to augment your quest experience.
Before anyone asks - yes there are archived copies of old addon versions both on our github repository and on several of the addon sites we use, and these will continue to be available after Cataclysm comes out, so you'll be able to get those old files if you really want them. I'm not going to bother making these more easily accessible unless you give me a very good reason. "I'm on a private server and I need them since we didn't upgrade to Cataclysm" is a BAD reason - and it's illegal.
From my understanding, the world boss is always there when your faction controls the Warfront. Like other world bosses you can only get gear from him once a week. There are other world bosses in the zones outside the warfront and 1 spawns a week just like Legion. I’m not 100% sure that the warfront will be available on launch but I have yet to read anything that says otherwise. The quest also reset once a week as well. Think of Warfronts like old Tol-Barad
K Kael'thas Alliance Kael'thas Horde Karazhan Alliance Karazhan Horde Kargath Alliance Kargath Horde Kazzak Alliance Kazzak Horde Kel'Thuzad Alliance Kel'Thuzad Horde Khadgar Alliance Khadgar Horde Khaz Modan Alliance Khaz Modan Horde Khaz'goroth Alliance Khaz'goroth Horde Kil'Jaeden Alliance Kil'Jaeden Horde Kilrogg Alliance Kilrogg Horde Kirin Tor Alliance Kirin Tor Horde Kor'gall Alliance Kor'gall Horde Krag'jin Alliance Krag'jin Horde Krasus Alliance Krasus Horde Kul Tiras Alliance Kul Tiras Horde Kult der Verdammten Alliance Kult der Verdammten Horde
With the level cap being raised in each expansion, new players are faced with a rather long and dated leveling experience until new level cap is reached. Blizzard already implemented stat squishes through the Battle for Azeroth 8.0 pre-patch last month, and has further lowered the amount of experience required to level, but even Blizzard believes that new players aren’t getting the leveling experience they deserve.
Recently, Blizzard provided their own WoW Token system for players to buy and sell World of Warcraft Gold. However, the constantly fluctuating supply and demand means that prices will vary. Consequently, getting the best prices isn't guaranteed, nor do you know when you'll make a sale. You also can't trade or resell any tokens you buy, as they become instantly "Soulbound".
Full disclosure on my time with Battle for Azeroth thus far: I leveled a Horde character to 120 and completed all three Zandalar storylines plus put about 20 hours into end-game content. I have also leveled an Alliance character partway through Kul Tiras and completed portions of the Stormsong Valley and Tiragarde Sound storylines. My only experience in Drustavar has been through the eyes of the Horde thus far.
The zone you start in isn't under your control, in as much as it's pre-selected for you based on your race. But for leveling purposes we want to make scaling work for us as much as possible. That means sticking to the lower level zones. Even though scaling will increase the level of the quests and mobs in those zones, the layout and design of them is built for a player with no mount. So you'll blaze through them and gain more exp/hour than higher level zones which assume you DO have a mount.
My toon was a monk, a class that gets extra experience for an hour at a time. I picked at it more than I have in the past, so I benefitted more from the 150 percent "rested" experience bonus. If I wanted to run a dungeon for quests, I fired up a high-level character on a second account and dragged my little toon through them. And having leveled dozens of characters to 100 and 110, I knew every zone and every objective.
The older brother of this potion originally came about in Cataclysm as the Potion of Treasure Finding, and is actually one of the best ways to make money. Since most Pandaria mats are constantly farmed, they usually sell for less than the Cataclysm mats. This makes using this form of the potion more effective for making gold. Not to mention that creatures die faster to level 90s since they were made for the previous expansion, making farming the treasure chests that drop rather easy.