You can make gil even not as crafter/gatherer. Crating/gathering only sometimes help you get gil faster. You may:
- farm dungeon for mats that sell well (there are some pretty rare mats that can sell for mil but i think they require quite of luck)
- spiritbonding and sell materias (you can get hundred thousand gil per day, or even million gil depends what kind of materia you get)
- challenge log
- GC leves (get GC seals -> buy GC mats -> sell)