Thank you for trying it out! Yes, you can press 1 / 2 to attack with the front row characters, and shift+3 / shift+4 to use spells from back row characters. It maybe takes a little getting used to, but I hope you have fun with it if you give it another try :)
Amplifier actually increases signal gained from walking/exiting floors. Every tile you walk gets a little amount of signal separate from passive signal (increased via "signal boost"). It could probably be clearer in the UI for sure
That's really fair it was quite tough to balance. I might revisit in the future and improve the content/ending if there's interest. Thanks for trying the game!