If you just care about unlocking the ability to fly in the new expansion, and you should, the site’s Pathfinder tool is a must-bookmark. Its Character Planner is also incredibly useful for getting a sense of what you could (or should) do next, based on your recent activity, the gear you’re wearing (and would like to upgrade), achivements you’re close to unlocking, et cetera. If you want a simpler guide, the site also has a great list of all the activities you should be doing each day and week in Battle for Azeroth.
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.
I like his recommendations 2 level 1-20 zones to get to 20, then do all the 2nd zones since they are designed for walking (Horde: Northern Barrens, Silverpine Forest, Ghostlands, Azshara, & Hillsbrad Foothills if you need a little more. Alliance: Westfall, Loch Modan, Darkshore, Bloodmyst Isle, and if you need a little more Redridge Mtns, or Duskwood). Don't even bother with the higher level areas, too spread out. Finishing up a Monk now and I had done all these zones before the update, the running between quest and the 50% experience cap is driving me crazy.
If you’re jumping back in for Battle for Azeroth, we recommend checking out the big “what to do first” guide from Wowhead. You’re also going to want to brush up on specific advice for your class—both Icy Veins and Wowhead have incredibly detailed guides for all of the game’s combinations of classes and specializations. Make sure you go in and figure out all the new (or changed) talents you’ll be using, and start to memorize a typical combat rotation so you don’t die nearly as much in game’s latest incarnation.