WAY ahead of yourself. And I don't mean that in a bad way, it's just that anyone JUST starting a 10 year old game can't expect to catch up and be ready for endgame in a month or 2, regardless of whether or not you can level to 99 rapidly.
Took me about 10 months
But seriously, I started January 1, 2011. My first capped job was THF - I got to 90 (cap at the time I think?) in like seven months. CLEARLY I WAS DOING IT WRONG. (Not really.)
I didn't step FOOT into Abyssea till I was in my 80s and actually I'd wanted to finish another LB before going but someone I knew had space and... Do you want to get to Jeuno and start collecting stones fast - YES. Actually doing stuff in there on your first job... errr not so much.
The LBs are all basically soloable now, but still need to be done every five levels past 50, so much of the benefits of quick Aby EXP would be killed by having to do them. Now, once you get to 75-80 - oh, you want to level in Abyssea. Heck, that's clearly what SE intended at that point though they've added alternatives outside.
Gusgen is marvelous and you can stay there forever, but I'd recommend leaving in the 30s - around 35 or so. That puts you in a better range for a CN party and doesn't leave your skills completely in the dust. And I can tell you from experience, don't stay in CN much past 60. The exp slows down, you won't be skilling up and you will get mind-numbingly bored.
And I will admit right out, the slog from 60 to 75 isn't the funnest. But there is so much stuff you can do while getting those levels! Aur and I were doing missions (ALL KINDS) as a lot of that content was geared to under 75 anyway. We unlocked EVERY job. We got so so so many maps. We did Besieged like crazy - and then they UPPED the rewards and it was even better! (Note, also a good place for skill-ups, just expect to die a lot as a DD.) Campaign once you get to 75 - no skill-ups (BOO) but they also upped the exp/AN rewards, and I did a lot of my post 75 leveling there. (And got a Medal of Altana to boot.)
So basically - don't worry about low level gear save quested stuff, do your missions to unlock areas and Dynamis, start getting stones, and level your first job as you go along.
Then LATER you can burn 10 jobs to 99 lol. (Disclaimer - I have not burned 10 jobs to 99). (Double disclaimer - when I do, WHM will be one of them.)