While it’s clear that Blizzard is eager not to spoil the future of Battle for Azeroth, it seems pretty unlikely that players who want to be pure evil will ever get their day to shine in World of Warcraft. Despite the decision being added into the game, the good guys will likely win and the threats to Azeroth will continue to roll on by, getting knocked out by players one at a time.
To achieve reliably 200% success rate, you need 1 champion equipped with Vial of Ofuscation (counter stealth missions), and the others can equip the +10% increased success rate per troop (some champions, like Falstad/Rexxar already have this passive and will stack). You want to counter the cursed status (success rate wont go over 100%) but you can skip increased time and additional costs affixes since they dont really contribute to success rate. Overall I would say that you need 1 Vial, 3 10% per troop Horns and either one 10% increased chance or one reduced duration item (it counters first strike missions). Using this setup, you will raise dramaticly your success rate which in turn will give you more rewards, but you will burn War Resources since you want to send troops to raise the success rate and we dont counter the increased costs affix most of the time. Its hard to evaluate how many missions you need in order to make-up the costs of the champion equipment, but in the long term is going to be worth.
If you want to spend as little time on your alt as possible - just do Legion Invasions. You can use sites like (https://wow.gameinfo.io/invasions) to track when the next invasion will be. Log in, fly to the closest world quest, and once there - right-click on the quest's name in your quest log and "Find Group". Sign up for some group, or if there's none - just start your own immediately, and people will come to you. It is 10 times faster to do invasion quests in a group. Once that particular quest is complete - leave the group, and fly to the next one, where you should find another group. Don't expect the group from one world quest to follow you to the next. Then you simply log out until next invasion. You can do 1-2 invasions a day, and each invasion will give you about a level or 1.5 of experience, if you have full heirloom gear. Each invasion will take about 20 minutes.

Any item with a grey name is considered vendor trash or poor quality. White items have some use such as tradeskills, spell reagents or reputation raisers, so you may want to check to see if they're worth more than the vendor price. Keep your eyes out for regular quality weapons, as even the worst of these tend to sell for several silver, or several gold at high level. Always check the tooltip for the vendor price before discarding anything. Also, white (or even grey) shoulder armor under level 20 sells regularly on the auction house, mainly because there is nothing better available at that level.
Soloing an instance can be all the more profitable if your character is an enchanter. During any solo instance run, you'll end up with some items which can be sold or traded, and some that are bind-on-pickup. Non-enchanters can only sell these soulbound items to a vendor, but an enchanter can disenchant the bind-on-pickup rare items, and then sell the shard/dust/essence instead of just selling the blue item to a vendor. (A side benefit of selling enchanting materials is that they do not require a deposit to list in the auction house, allowing you to list endlessly until the item sells.)
Anyway both got to 110 at around 50h played. I messed up with my Pal by going to Legion once I hit 100 instead of finishing treasures and bonuses in WoD. All in all, if I picked the best zones and was only trying to level as fast as I could, I would probably could have done it in roughly 40h. Note that it would have a been A LOT faster with a Monk as both Ret and Rogues don't really have a decent AoE until 40+ (45 for Ret and 63 for Rogue I believe). The daily also helps a lot. I know that leveling my Monk before the pre-patch was insanely fast. Might be slower with the changes to FoF, however.
Players’ relationships with the NPCs around them have been hit-and-miss over the years. One of the original issues with Thrall, the Horde’s original Warchief, is that players began to refer to him as “green Jesus,” because of how infinitely powerful and infallible he was. But he’s been gone since the Warlord of Draenor expansion, and with the death of Varian Wrynn and Vol’Jin at the start of Legion, the old guard hasn’t been there to guide players the same way as it used to be.
Skinning is both highly profitable and convenient, in that you will be skinning the monsters that you're already killing as you level. A skinner starts by collecting relatively worthless ruined leather scraps, but soon moves on to light leather, which can be sold for a good profit. An excellent way to farm leather is to skin the kills of other players, especially if you are following along in the wake of a group. However, do wait to start skinning until it's clear that the other player has abandoned the kill. Don't assume that the other player doesn't skin just because they are not a leather-wearer, for example. Note that your chances of getting a better grade of leather increases with your experience; it is possible, though rare, to get light leather from rabbits. Higher grades of leather yield higher profits. A skinner/miner has potent earning power through the auction house, but often runs out of inventory space.
Alchemy is a great profession for gold-making as the main outputs are consumed on use, this means that there will always be demand for new potions and flasks. The old world recipes are also very profitable. Sadly I don’t have Legion alchemy so I can’t personally help you. The best guide I was able to find on the internet is this video guide by Ninja Kuma.
Game director Ion Hazzikostas told Kotaku that the team plans on turning every one of the game's servers into PvP servers. However, everyone will need to opt-in to PvP combat if they wish to participate in battle. The catch is that players will only be able to turn PvP on or off inside of major cities. Out in the wild, you'll live with the decision you've made. 
From “The Burning Crusade” expansion, weapons like Klinge der Zauberei, Die Nachtklinge and recipes for different weapons are really valuable. The best example is Pläne: Teufelsstahlangschwert, worth 500.000+ Gold. These items are World Drops, you can find them in all raids and dungeons. I don’t know any Open World Drops, but that does not mean there are none. Another great transmog source are world bosses and rare spawns on Outland.