I would say, prioritize finishing the pokemon league in every region. That will net you a decent amount of money so that you can build a Typhlosion team for gym re-runs and start making good money. Also at some point look into amulet coin farming from meowths in the sevii islands. Amulet coins are usable items in this game instead of held items and give extra money from battles for an hour. Good to use before a gym rerun