Get Lyric and Laka as quickly as possible. These two will make you rich.
Put Lyric with cards that increase item drop and gils drop in your combat team. That should solve all your gold problem.
Laka keep stealing equipment for selling later.
I think the best spot to farm is where your Laka can steal first then one or two of the team can wipe the enemies off in turn one BEFORE the enemies can act. Which change rapidly according to your skills. (i.e. Vera's summon, the others' AoE magic)