Multiples of three in four chips. Three has the most number of multiples without accidentally using too few chips, and four is so that you'll last long enough to not run out of chips and break your combinations.

Two Dark Knights and an Alchemist. Spam Darkness and Stash-->Mega-Potion, or Mix-->Potion/Hi-Potion. Set up by casting Light, Lunar, and Star Curtains. Shouldn't be too hard, just long. If the battle drags on too long, you'll notice that your attack output decreases. The only cure is death. And death is death, so ignore it, and continue to hold down the X button while you focus your attention on things that are interesting.