How do you level more than 3 "Fighting" Classes if there are only 3 starting areas?

[Bixby]

So basically with my level 1 Conjurer, I need to start killing ladybugs...non-stop...

You start killing whatever your hunting log asks you to kill. You also participate in any FATEs you come across, and maybe burn a few leve allowances. You're level 10 in no time and can add in guildhests, and then dungeons when you hit 15. From then on, you do FATEs if there are enough people doing them in your level range, and you queue for dungeons, while burning leve allowances and/or participating in FATEs and/or grinding chain bonuses on mobs your level while you wait on the queue. Add in the daily roulette, which will get you one level a day on its own up through the low 30s.