Neat little management sim.
I like that there are random events to respond to.
Very minor point about the UI: there's no reason to have the option to send 0 mana, as the minimum value that has any effect is 10.
Did you consider just letting the player click a hex to send 10 mana at a time, rather than using a menu? It would save clicks, but I guess it would also be more prone to player error.
Grats on your game :)