Each of those modes existed long before this latest expansion; raiding is a basic concept in MMOs, and Mythic+ was added in World of Warcraft’s last expansion. The problems with Battle for Azeroth’s endgame come from the systems it adds, which most often artificially gate progress where most of the fun can be found. If raids and Mythic+ are the carrot, we’re about to talk about the stick.
The Hearthstone has a cooldown of 30 minutes, but there’s a guild perk called Hasty Hearth that shaves the time by half, giving you a strong incentive to join a guild. Yes, even if it’s some random guild that invites you without warning. It may feel odd to join people you don’t know, but if they have Hasty Hearth (and most guilds do), joining can save you a lot of legwork.
If you queue as a healer - take care to always have a stack of water of appropriate level. You can buy it at an innkeeper for next to nothing, but remember that it will become too low-lvl for you very fast, so you need to buy new water every 10-20 levels. Alternatively, you can buy a stack of every tier of water in Stormwind, and just always carry it with you. Another alternative, if you see a mage - always ask him (politely) to create a table for you. Grab 2-3 stacks so you have extra for the next runs.
The Alliance are able to unlock the void elves (exiled blood elves who can tap into shadow magic, trained by Alleria Windrunner after her experiences on Argus), Lightforged draenei (draenei members of the Army of the Light who fought the Legion on Argus), Dark Iron dwarves (fire-blooded cousins of the in-game dwarves of Ironforge), and Kul Tiran humans (larger, more heavyset versions of the in-game humans of Stormwind).
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.