I also noticed that the slowdowns were heating up my graphics card (a GTX1080 with good cooling and a well-configured fan curve). On high but not max settings, I would always hover around 60-65 degrees C, and thought this was normal. After turning auto zoom off, I noticed that my card never gets past 49 degrees C. I'm pretty shocked, as it's a very hot day where I am and I didn't know one feature could affect temps so much. I didn't know my temps could even get that low! Even on full max settings (with 200% resolution scaling etc.), it now can't go over 66 degrees, whereas it used to go up to 74 degrees at times when auto zoom was on.

Yes. I believe so. It plays nice with most Addons; even many that are out-dated. The only Addon with known issues is the mini-map in Bandit's UI (the rest of Addon works well with this Addon). The issues with Bandit's mini-map are fixable by disabling its mini-map (how to do that https://i.imgur.com/2zl3IEV.jpg) and using Fyrakin's Minimap. I found no issues with Fyrakin's Minimap. I have not testing other mini-map Addons but I assume the results should be like Fyrakin's.

A dungeon should take about half an hour to 45 minutes, that is reasonable. What did we do to Maw of Souls because it was by far the fastest dungeon to spam run for AP? Nerfed its yield. Same happened to dungeons. Except instead of nerfing the XP, they adjusted the clear speed to justify the experience a bit more. Is it perfect? Nah, a lot of dungeons aren't even that long with updates. At most a clear takes 5 mins more.
I have tried it a few times. It's good if you're new to the game. Otherwise not so much. I found I leveled slower by using it, as it's suggesting to take the longest possible route usually. Basically following roads everytime, when you could take an easy shortcut. Especially if the shortcut involves a bit of fall damage, it's out of question. The "go here" spots don't also update if you take a shortcut, and then the waypoint arrow points to wrong direction. But perhaps it has been updated since then.
While it’s clear that Blizzard is eager not to spoil the future of Battle for Azeroth, it seems pretty unlikely that players who want to be pure evil will ever get their day to shine in World of Warcraft. Despite the decision being added into the game, the good guys will likely win and the threats to Azeroth will continue to roll on by, getting knocked out by players one at a time.
Tiragarde Sound and Stormsong Valley are both fairly similar zones, but Stormsong is a little longer, meaning that you might not even have to finish it to hit 120. Tiragarde also comes with a bit of a warning. There are plenty of side quests to do in the zone after you finish the story quests. Don’t do them. It’s not worth the time or the experience you’ll get.