Gold sellers would steal players’ account information using keylogging malware and phishing scams, so they could strip characters and harvest everything of value. They used stolen accounts and the accounts of players who had paid for “power leveling” services to “bot” for resources, using automated cheat programs to harvest resources that they could quickly liquidate on the in-game auction house. This caused the price for traded goods to crash, which impacted the entire economy.
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.
For Alliance it's Lok'Modan, Redridge, Darkshore, Felwood, Stranglethorn (both parts), Plaguelands. Somewhere between 3 - 3.5 of these get you to 60 in like a 16 hours /played, if you queue for dungeons at the same time. I recommend dropping everything at 45 and going to Darkshore-Felwood if you didn't do them yet - they are literally the fastest levelling zones in the game right now, maybe only trumped by Silverpine.
You can have a maximum of 25 quests on 1 toon. Starting fresh (0/25 quests) on a toon will be beneficial at the start of a new expansion. ahhhh a fresh start. On the flip side, stocking up with 25 completed quests, ready to turn in, might be beneficial too. As soon as BFA launches, turn them all in for a great small boost to EXP before you even step foot into the new land.
Something to keep in mind as well is that this will make enchanting materials more valuable, since it is likely most players will now simply scrap their boe greens instead of getting them disenchanted. Also redundant dungeon/raid gear can be scrapped rather than traded to the (guild) enchanter in the run. Less stuff gets disenchanted, meaning there will be less ecnhanting materials, meaning their value will rise. All the more reason to DE rather than scrap as an ecnhanter.