Through out the game, the quest log will be capped to 20 many times. The guide makes use of maximizing the total amount of quests you can accept at once. Because of this it is important to follow the guide exactly and only accept quests if the guide tells you to so you won't run into issues not being able to accept a quest. If you do accept a quest that is not listed in the guide, write it down because you may need to abandon it in order to keep following the guide if your quest log is full.
I'm not all that hardcore on "Classic", I want to relive the old zones and the old world and it seems like most people I'm taking to is feeling the same. We would prefer to have quality of life improvements regardless of them actually being in the game at in 1.12.2 or not. Like the "Automatic Quest Tracking" to actually track it properly without you having to actually trigger progress in the quest for it to show up would make perfect sense. It's no real need to make such a thing behave nonsensical just because it's "authentic".
With the Classic beta now out it seems every related article somehow manages to spark the eternal war of "Vanilla was the best WoW sucks now" and "lol nostalgia goggles, Vanilla sucked, enjoy your two weeks of Classic". I have to say, even though I understand the principles behind the battle and the reasons people behave and talk this way... I actually REALLY don't get it on a deeper level.