Messing around on my 2nd playthrough-
Vaan is Knight as first job...
1) Start game and play it to Rogue Tomato Hunt, finish that and go back to Rabanastre
2) Farm pots in Estersand by the zone to outpost for Phoenix Downs, I got about 30
3) Head to Westersands and pop Dustria. 1 Hit KO Dustria rare monster with a phoenix down and zone out before dying animation ends
4) Repeat until out of phoenix downs
5) Should be lv15-20, farm stage 1-2 for diamond armlets to buy all monographs (takes about 27 diamond armlets) and steal phoenix downs from rats/thextra + 1 phoenix down from pot in stage 2
6) Should have about 50 phoenix downs, spend it all on dustria again
7) Lv22-25 at this point, go get Penelo by starting Sunstone quest and teach her Fire
8) Try to steal Karatka from Stage 3 flower cactoid, farm LP to unlock it (for your knight)
9) Should be able to beat trial 1-10 at this point, farm as needed for licenses, etc
OP team in the beginning of the game, especially since all characters that join your team will be nearly lv30 as well.
I don't recommend this since just playing the game will be more efficient but was a nice way to get levels before leaving Rabanastre, lol.