The Heart of Azeroth is an artifact given to the player character from the world soul via Magni Bronzebeard. It is a necklace that can use the power of Azerite, the lifeblood of the embryonic titan Azeroth (See Plot, below). Azerite is similar in function to Legion's artifact power, in that it is gathered normally from playing the game and is used to upgrade an artifact; likewise, the Heart is similar in function to Legion's artifact weapons by having the capacity to be constantly upgraded. Unlike artifact weapons, however, the Heart is shared with all of the player's specializations and can empower all eligible pieces worn simultaneously.
The Horde will now control most of Kalimdor, and the Alliance most of the Eastern Kingdoms. For a low-level character the quests and storylines won't change, but for high-level players many zones will see changes via phasing. Teldrassil is burned and Undercity is in ruins as the story progresses by phasing. At max level Arathi Highlands and Darkshore are phased to be updated to reflect their status as locations for Warfronts.
All I know is that Scribes are going to make bank with those Contracts. All guides talks about them and everyone will want them. Better ride that money wave while we can. Other than that, Alchemy and Jewelcrafting are always safe bets with tradable and marketable goods. Engineers can get an item for followers to bring back more Azerite, ot sure how much of a headstart that's gonna give them. The rest of the professions honestly looks kinda lame since most of everything is BoP anyway.
Yes, that is easy, but it's not quick. Further down in my comments to OP I detailed the GIO farm, and reasonable yield expectations. I looked up a few guides/videos before commenting and most of them estimate a yield beween 800-1,000 GIO/hour. That lines up with my past experience with it as well. That'd be, taking the high yield end, 4.2 hours to farm the GIO for one toon's monthly needs.
It is really, really a stark change of pace from WoD and Legion where just questing and killing things would result in at least a small but decent profit from a day's activities, typically of at least 1k and often 2k. But now to get that sort of return, I have to really focus on gold WQ's, not spend any money on anything that I don't absolutely have to, and do 45 minutes of Legion content.
At the end of Legion, the titan Sargeras was imprisoned, but not before he plunged his sword into the planet Azeroth. This not only devastated a massive area (much of the desert zone of Silithus is now cracked and scorched), but badly wounded the gestating titan inside. While the heroes managed to ablate the worst of the damage (at the cost of the majority of their artifact weapons' mythic power), the world is still wounded and bleeding a substance called "Azerite," which has great magical potential. The Horde Warchief, Sylvanas Windrunner, attempts to consolidate Horde power on Kalimdor and gain a monopoly on Azerite (which is primarily found at the southern end of the continent). Her campaign to do so, the War of Thorns, formed a pre-launch event for the expansion and ends with the major Night Elf holdings on the continent seized or (in the case of their capital city of Darnassus) annihilated. The Alliance makes a retaliatory strike against her home base, the Undercity, which was formerly the human capital of Lordaeron. This succeeds in driving the Horde out, but before leaving Sylvanas saturates the area with disease and toxins that render it uninhabitable. With this tit-for-tat military exchange, the Horde has almost complete control over Kalimdor, while the Alliance has near-total dominion over the Eastern Kingdoms. With further conflict inevitable, Battle for Azeroth takes the two factions to the continents of Kul Tiras and Zandalar to recruit new allies in order to turn the tides of war.
The hexweave bags are still a safe bet unless the new 32 crafting cost is like 10% of them. The one thing I'm more concerned about is the professions squish. This will make the old world items that we've been selling (TBC Dust still sells by 200 stacks easily) only required for Transmog and not leveling. This was a better option for a lot of professions (especially enchanting). Expecting their near-death with the next expansion. :(
Honestly TL:DR of any guide. Is learn your markets, it's as simple as that. Learn who's in it, learn what's profitable, watch different time tables. I've earned 2 million profit OFF 1 market and half set up TSM. I've barely tried before this I was a hardcore raider, only made gold over the years through BOE farming and run sales (which are goood, don't get me wrong) but I want to be making the multiple gold capped characters.
The expansion brings a major change to the PvP ruleset on each realm. Every realm by default only allows players to attack NPCs in the open world; players who wish to engage in world PvP now have a setting called "War Mode" that can only be toggled on or off in their faction's capital city (i.e. Stormwind for the Alliance and Orgrimmar for the Horde). While in War Mode, players have access to new talents and abilities, as well as a slightly accelerated rate of XP gain. Characters with War Mode activated are only able to see other players with War Mode, unless in their own capital cities.
When an allied race has been unlocked for a player, new characters from that race will start at level 20. If a player levels an Allied race from 20 to level 110 without using character boosts, they will be rewarded with a unique "Heritage Armor" for transmogrification that reflects the unique lore behind the race but is limited for use to that race. Doing the quests to unlock the allied races will also unlock the races' unique mounts for use by the characters of their faction. The void elves, Lightforged draenei, Highmountain tauren, and Nightborne, as races tied to the storyline for Legion, were made available with the preorder on January 30, 2018. The Dark Iron dwarves and the Mag'har orcs are made available upon completing the "War Campaign" in Kul Tiras and Zandalar and reaching Exalted with one faction's War Campaign reputation; the Kul Tiran humans and Zandalari will be made available later in the expansion. Game director Ion Hazzikostas also indicated that additional Allied Races may be available in the future.
Consumables (Alchemy, Jewelcrafting, Enchanting) – When I have gotten a toon to max level and managed to get all of the end game recipes/ranks, I have done well. However, I never have much luck with the lower level items. It feels to me like if someone is going to buy a gem, enchant, or flask, they want the best one or none at all. Maybe that comes down to the servers I play on, but it does make sense compared to how I play my own toons. I either am going to gear up a toon for endgame or not worry about it at all. Alchemy does have the benefit of transmutes which even the low level ones can make some decent gold. JC does have the MOP mounts and pets if you can get the recipes for them but otherwise these professions feel like max level or bust to me.
There's a few profession crafted pets in BfA on the horizon - Battle for Azeroth Tailoring is getting a Hot Air Balloon style pet, and BfA Alchemy looks to be getting a brand new Transmute Meat to Pet. There are some mount buff consumables from both BfA Leatherworking in the form of a mount barding, and Blacksmithing in Battle for Azeroth will be able to craft Stirrups and Hoofplates to increase mount speed and allow you to interact with things while mounted.