Thank you so much for this detailed feedback, it means a lot to us!
We'll be adding more ingredient combinations to mix and visual feedbacks to make sinergies more intuitives. We currently have 5 mixing combinations available (Ice Golem, Fireball, Rain, Meteor Rain and Thunderstorm), and we agree that almost every mixing should be a valid recipe (just like it is in Magicka).
Awesome suggestions regarding the shop, drops and keyboard inputs! We'll definitely take all this into account for our next updates.