Completed 4 so far, leveling very slowly my 5th alt. Honestly, for me leveling alts feels much better than in WoD/MoP, but I always prepare for that to get (close to) unique experience. Overall I think we are so used to questing by doing World Quests every day, so doing few more to level alt isn't big deal. So, to level next alt:
1) I always check first what zones/dungeons are needed for my campaign, and I always focus on them.
2) With rested experience and order hall misions (I spread my leveling on few weeks), it take usually two zones with dungeons to reach 110.
3) I do all avaiable class quests, including alt artifacts, before 110.
4) After 110 I focus on finishing class campaign, I have around 12k order resources after that, so my alt can buy all 25 knowlegde on his own.
I don't touch professions/Suramar on alts so far, but soon my first alts will have 25 AK (knowledge catch up exist right now, imagine that), so I may switch to one of them to do some stuff.