The achievement description isn't very good. I think you need to maximize your star coins in all 3 modes before the achievement will count. To get star coins, kill enemies while using a card; all their shots will turn into star coins and get sucked in.
Single play: I found it easiest to hit MAX (2500 coins) on Mind Blowing difficulty, surprisingly. There are so many shots that you'll hit MAX in either the first or second level. Use Louie since her barrier lasts so long. Buy 3 cards from the shop each time you visit, and use them immediately, leaving your barrier up as much as possible. (Note that entering the shop refills your magic, which is handy!) A handy trick if you're getting hit before you reach MAX is to lose two lives right at the start of the game, before the first shot. This is because losing a life reduces your star coin count by 25%, but continuing doesn't! Strange but useful.
Score attack: Really easy to hit MAX (5000 coins) on. Play 5 minute mode with Louie, leave your barrier up as long as possible, and keep entering the shop and buying cards. You shouldn't be in much danger since the shop comes by so often.
Boss attack: Annoying to hit MAX (2500 coins) on. You basically need to get up to round 7 or 8 without getting hit more than once or twice, killing each boss with a card. See my boss attack achievement guide for some good Louie strategies (mostly for bosses past round 10, but they should still help for killing these much easier versions safely). It's a bit annoying killing the snake boss (boss 3) with a card, so don't bother, which gives you some spares. For bosses 5 and 6, you might want to leave them alive with a sliver of health while your barrier accumulates shots, since they'll all turn in to star coins when you kill the boss. (You can often get 300-500 coins from a boss 6 kill this way.)