Returning player from 2011 levelling questions

I don't have my old account anymore so I'm just starting from scratch. I don't have any intentions on LTS-ing because back when I played for a couple years I only ever had time for about 3 characters anyway so I just bought the FF 3-pack and called it a day. My question is about levelling my 3 freeforms. What I can't remember is whether or not I'll miss any important unlocks if I just pass on doing all the zone missions for leveling and just keep repeating the adventure packs to 40 instead. The reason I'm considering doing it that way is because of questionite. I figured getting a head start on my supply while leveling might be a good idea? So far all 3 of my freeforms have been capable of soloing easy packs like Serpent and Whiteout.

I've read that this is something a lot of people do now, so I just wanted to check in and make sure I'm not going to miss unlocking anything major by skipping regular mission content in the zones.

edit: forgot to mention, the reason why I want to farm questionite as soon as I can is to buy Merc gear, and buy more stuff from the questionite store, not to exchange it for zen because there's not really any zen purchases I need other than a hideout and I'll just pay for that.