What's the spending strategy for the Magic Wheel? (Legend Skin)

Been wanting to get a legend skin for a while now. Any tips on how I should approach this?

I already know about the magic potion strategy, where I should only use them when I have 5 so I can claim a free potion in the magic wheel rewards. But that's about it. Haven't really spent any money in this game, and I've also noticed some bundles can only be bought once within a time period. So I'm not too sure about the diamond bundles and which one has better value.