I do not recommend going for this until you are at the Medieval Age which is when I went from 50% to 100% not that I was exactly trying but it helps.. A TON.
Bonus's do not count towards this achievement meaning if you get a 50,000 coin bonus from your league 0 will go towards the achievement. Only what you steal from an enemies base counts. I recommend (unless you already have the 2500 trophies achievement) going for 1 star when attacking someone with a ton of coins, also try aiming big, I aimed for 10k or 20k's.
Confirmed by AP E JC
Coins you earn from the campaign do count towards this achievement.
How to earn a ton of free Jewels:
Let me know if you have any questions.