You can access the Golden Saucer at lvl 15. Look up "Challenge Logs" and unlock them as soon as possible; you have no idea how much it helps. Also, do the quest to get a racing chocobo, because many of the Challenge Logs require it.

Even the biggest Logs, the best way to get MGP, give you 10,000 MGP per week at most, and the whole I would say isn't giving you more than 50-75,000 altogether per week. It will take you months to get to 1,000,000.