When you have completed your third zone, you should be nearly max level, but you still have work to do! Head back to your faction hub and complete the last foothold quest to unlock your fourth mission table champion. After, you will want to do your newly available invasion missions for your faction. This quest chain is one that will be time gated by reputation levels earned with the 7th Legion for the Alliance and iThe Honorbound for the Horde. Complete as many quests as you can and then finish up your leveling with side quests you may have left in previous zones as necessary.
Warlocks have received new spell effects; all the other classes received new effects in Legion. Male orcs are now able to toggle between the initial hunched posture and standing upright by using a barbershop, but the other races are not able to toggle between two postures. There are new druid forms for the allied races, i.e. a Zandalari troll forms are all dinosaur-based, while the Kul Tiran humans take forms made of wood and bone as their teachings come from the Drust people who populated the land before them rather than the Cenarion Circle.
At 98 you have the option to drop what you're doing and return to your capitol city to start the quest for your Legion Artifact weapon. However, I do not believe this is necessary to do right away unless you're struggling with kill speed in your current gear. I would recommend waiting for a natural pause, such as hearthing to repair and clear your bags. From 100 to 107 you won't even really fight mobs that often; only just enough to clear the way to any treasure you need to pick up.
Potions serve more utilitarian purposes, and it's up to you to decide whether to make use of them. The most common is the Swiftness Potion, which can provide you a handy boost in speed while going after annoying quest objectives indoors. These are generally MASSIVELY overpriced, because people know how useful they are. I opted not to spend the gold since Warriors are already fairly mobile, but slower classes may benefit greatly from these.
For reference, my previous best time abusing Method-0 in 7.3.5 was 32.4 hours(as show in the old thread). A difference of just over 8 hours; which isn't all that bad, all things considered. And I believe I made several errors along the way, which could be cleaned up in future runs. I believe that that gap could be significantly closed by using a monk's bonus, but I hate playing monk...so...yeah. YMMV