The mission (quest) system in TSW is *very* different from nearly every other MMO. If you approach missions like you do in other MMOs, you might be disappointed. If, on the other hand, you *understand* the mission system and the design reasons behind it, you might find that you really enjoy it.
Don't think in terms of "quest hubs". Don't try to finish all the missions that are available at the first apparent "hub" you come to. That's not how this game is designed.
Also, don't think in terms of "I need to rush through all the zones to get to max level and the endgame." The endgame literally starts in Kingsmouth. Seriously. Yes, there is a short vertical progression whereby you get progressively stronger, but don't obsess over that. It will happen quickly and organically while you play the endgame, which starts the moment you exit Agartha in Kingsmouth.
Instead, understand that the multiple missions available at given "hub" are meant to *spread out the players*. They're not a laundry list of quests to complete first. If there are 4 different possible quests at a given hub, take your pick of one and follow it to the end. Meanwhile, other players are making different choices and the end result is that 25% of you go to one part of the map, another 25% go to a different part, and so on.
The next important thing to understand is that when you finish the last tier of a quest, STOP RIGHT THERE. Do not run back to the hub. Just phone in your reward right where you're standing, and then start looking around the current area carefully. In most cases, you should find some other "mission starter" of some sort very nearby. Usually within 50m of where you ended the mission you just finished. Take THAT quest and follow it to the end.
Now keep rinsing and repeating. Eventually you'll end up near that first "hub" again, and since it's nearby, that's the logical place to pick up the next mission.
LET the quests give you a tour of the zone. Your tour will be different from other player's because you're making different choices.
If you find yourself running back to a hub to grab the next quest from that hub, *you're doing it wrong*.
If you don't find a new mission starter within roughly 50m of where you ended the previous mission, report it as a bug. Seriously.
Now as to your queue:
There are three "activity mission" types: red (action), yellow (sabotage), and green (investigation), you can have only one activity mission in your queue at one time. These are typically given only by NPCs, and most (all) such NPCs are marked on your map.
There are also "item mission" types, which are a grayish green with stripes along the bottom. You can have up to three of these in your queue at any one time. These do not appear on the map, and they can be anywhere in the environment. You might want to mark them with a map marker when you find them, in case you want to repeat them again later.
Finally, you can have only one "storyline" mission (blue) in your queue at a time, and only one "group instance" mission (purple).
Don't see the limited queue as a detriment. See it as a reminder to really follow the story of each quest instead of treating things as a mindless laundry list. And remember: where one mission ends, there is usually another mission to start *very close by*, and if not that's actually a bug worth reporting. Although be aware that you might have to look carefully for it like many of the "clue hunting" mechanics of the game in general.
One last note: you cannot "drop" a mission. You can only *pause* a mission by taking another one of the same type. To resume a paused mission you *will* have to find the original place it started from and "start" it again. However, when you do this you actually resume the mission at the tier you paused it at. Be aware, though, that if you did not fully complete that tier before pausing it, you will have lost all progress *within* that tier and be starting at the very beginning of the tier again.
