Hey Absolute, have a look at this link: http://flowerknight.wikia.com/wiki/Shop

There are a ton of different currencies in FKG, I was so confused when I 1st started, but you'll get used to it. The shop restocks at certain times, so you can't just buy unlimited number of things (too bad!)

Dragons are good if you need to evolve girl. Manyus are good to lvl girls. Ampules give extra extra stat boosts, allows your girls to have stats over their max. amount. The cakes/bunny etc. items you can give to blossomed girls for 2nd affection. And OMG if you have 20k+ metals, you can get super awesome equipment for your girls, they are some of the best equips. in game (I think).