I leveled all classes in parallel. It's long but i was able to make gil from the beginning and i never bought gear and tools - could make it myself.
I used NQ gear and tools and sold NQ items till i reached lvl 30 - after this level there is no problems to produce HQ from HQ materials. Further leveling allows to to replace some HQ materials to NQ.
I used for leveling GC supply missions, but most of exp was from produceing items for sale. Also i used Ixali quests and leves to speedup leveling of bad salable classes - mostly cln, alc and crp... sometimes armorer.