very hard to estimate without checking exactly how many quests there are total and i personally dont know where that number is available

but considering a single level often has dozens of quests tied to it available this could easily take months. possibly a year. maybe more....

eitherway if you started doing it now, you could probably guarantee you would still being doing it by the end of this year.

as for class, ive seen somewhere that, for various reasons, SMN or DRG is more fitting for a story run [but dont ask me why i cant remember the thread]
and DRG is more so for the HW stroy for obvious reasons

So I'd say for story intertwining purposes go DRG.

cant help with server though
i think Data Centre is more important overall tbh