I just started and I'm so lost - Help!

[Bixby]

so is the general strategy focus on one class to 50 first and then start working on others? so like, should I even bother going into a different guild to get access to a new class yet, or only when I get archer to 50?

You'll need to take at least one detour to level another class to level 15. Jobs unlock at level 30, and each one requires a second class at level 15. For example, to unlock Bard from Archer at level 30, you need to take Pugilist to 15. Class Q&A Guide lists those, along with some other good info.

And you definitely want to unlock the job at 30. Taking up the job instead of the base class gives you a large boost to your main stat (DEX for BRD), and gives very useful abilities for party play every 5 levels.

There's also a second class that each job can take cross-class skills from, besides the one needed for the unlock. For example, Bard can take skills from both Pugilist and Lancer. It might be worth your time to collect some of the other cross-class skills before 50 as well. And when you get to level 50, you'll definitely want your full range of possible cross-class skills before you start getting into more difficult content.

Beyond that, it's really up to you whether you take one all the way to 50 before you work on the others. Contrary to what the in-game help tells you, you get the same 50% XP bonus on lower-level classes regardless of differences in level; as long as you're working on something that is lower than your highest level, you will get that 50% XP bonus across the board. For example, if your highest level is 28 ARC, both your level 1 ACN and your level 27 LNC will get the same bonus.

Getting to level 50 can make several other things easier; unlocking all the travel options, making gil to gear up other jobs, etc. But it's not such a vast difference that you'd look back on your life ten years from now and wonder why you ever allowed yourself to get sidetracked into leveling other jobs. Whatever floats your boat.

Regardless, there's no harm in at least unlocking any/all of the other classes at the guilds while you're there. You don't lose anything (except a little armory chest space for the starting weapons, more for armor and such if you actually start leveling them), and the only thing that's irreversible is the fact that they're unlocked (and leveled if you start leveling them).