but one thing: ampys give girls with the same color more EXP, so it's a little bit sad that there is no ampy for magic.

I never notice that. It's weird. But maybe. Anyway, exp giveng by ampy is just a bonus to me. Don't use them to level up your girls as first purpose if you want my opinion.

Dressblomm will be more interesting but... I'm not sure they will add them it the life crystal shop. So, we must just use them as best as we can. But since you're a beginner, maybe you should focus on manyu. Raise your level with cheaper stuff and then, aim for more expensive things. In any case, with more level and power, we will be able to farm higher level missions with more ease and get more and more life crystals. If you're lucky you can get 9 of them on ultime missions of the current event.