Welcome back!
It’s not you; it’s Blizzard! 
Lots of people who used the boost have exactly the same reaction.
But looking you up, the Rogue you’re posting on has 366-ish gear, wherethe boost gives you 424s. So you boosted a different character?
Yes. It completed the four original zones, opened World Quests, Forbidden Reach, and Zaralec Cavern. You can still go those extra zones, though, if for some reason you want to.
And yes, you should be starting on the Guardian of the Dream questline. Guide here: https://www.wowhead.com/guide/emerald-dream-comprehensive-guide-outdoor-content-rares-quests-21782
Make sure you have applied your Dragonriding Talents before you start!
None of the other quests you have are important, and what I would do is drop them all and refuse to pick up any more until you have completed the Emerald Dream. There are three weekly events there that drop 440+ pieces, upgradeable to 463, available from questgivers at the camp - those are your priority. You can knock all three out in less than an hour, so that is time well spent.
For any character that doesn’t have any 424s, you can do a Dreamsurge weekly, This week it is in Ruby Life Shrine by the Flight Master - see the big blue circle on the map. For gathering 100 Coalescence, you get a bonus token for a 428 piece - and you can buy a 415 piece with the Coalescence as well if you need it.
And ofc the AH will supply gear if you have the gold, and don’t want to wait.
This seems to be a straightforward “what to do after you hit 70” video that should apply to you, pretty much, though I’m not sure that Time Rifts are actually alive much these days.
Once you have established the weekly farm in the Emerald Dream, you can, if you wish, take the quest at the top of the Seat of the Aspects to do the Forbidden reach, and then the Zarakec Cavern, chains. These will not be giving you gear upgrades, but there are mounts and pets and achievements.
Please ask again with any more specific questions!
