90-91 i collected treasures that gave resources and then dumped them all in xp potions and began to clean up shadowmoon valley while also doing bonus objectives, after shadowmoon i went to gorgrond and did the same thing and then to talador for a bit before I was 96 and went to quest in arak until I was 98 when I picked up my artifact and went back for the last few levels. Overall 90-100 took like 4 hours.
I used to use his profession guides they really did help in the pre cata days (before WoW professions site was around) It's really up to you he does keeps his guides up to date and he does he homework (I still get emails) Their are some free leveling power leveling add ons to help you level much like the paid guides. Keep im mind I think he moved to a sub based plan and not a one time payment
Excess Potion of Accelerated Learning: Acquired in your Garrison (part of the Warlords of Draenor expansion), this gives you a 20-percent bonus to experience from killing monsters and finishing quests. It lasts one hour, but you can buy it multiple times and use it back-to-back. Alliance players buy it from Sergeant Crowler, horde players buy it from Sergeant Grimjaw. Does not work above level 99.

Though related, this is no longer true. You can now purchase a lvl 90 character boost. Some power levelers have hoped for a day when you could use real money to buy individual items in-game, some times called "micro-transactions." At a Game Developers Conference 2008, Rob Pardo gave a strong indication, Blizzard would not ever go this route with World of Warcraft.
As late as possible. Early on, you’ll want to follow the missions in Battle for Azeroth right up until you get the option to send a follower on a two-hour long quest. As soon as you get there, stop doing the War Campaign missions. You can come back to them once you have reached something like 119 and a half and finish leveling with those if you want. If you don’t use these missions to cap off your leveling journey, then they’re the first thing you’ll want to do once you reach max level. 
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