I played your game a bit. I am not sure I understand why “autobattle” part is needed as opposed to simpler turn-based combat.
The basic idea of combining as the main action definitely have potential. I would maybe even go so far as to extend it to consumables too, so combining becomes the only action for player.
I would suggest to implement “unselect” action and auto-remove selection after battle round. I lost resources many times due to accidental clicks.
I disagree with forcing player to remember all combos. On the contrary, I would highlight suitable resources and maybe even add hints on the result (although it would be hard fit into UI). Maybe add some special animation for activating the specific combo first time, but burdening the player will only result in unnecessary frustration. (IMHO, of course).
Also, the music is nice :)