Thanks for playing!
The slot machine being completely reflex-based was tried before and not popular at all. People were getting tired of trying to constantly time it, and it became a game where you're constantly in Quick Time Event mode, and the payoff between timing it right or not was so huge that you couldn't just give up on it. Making it fully automated would make the game a complete auto battler, with no player agency in battle. The current system is the best middle ground I could find, where you can time the first reel to nudge the odds in your favour, but the quality of the follow-up spins are random, lifting the pressure from the player significantly. Players who want an autobattler already have the choice to just mash the button immediately
Randomized starting loadouts will be an unlockable feature, and yeah, they probably need some refinement
Stacking one color is indeed one of the best ways to go, however there are enemies in the game designed to counter a specific color so I usually like to go 2-3 colors. Going for more than 4-5 colors will end up quite inconsistent unless all symbols are 2+ colored
I considered making money equivalent to health, so that you're trying not to go "broke" instead of having generic health, but I think that would take away too many health-based interactions.
Unlocks are completely arbitrary with no thematic reason. Kinda imitates Binding of Isaac in that way, where things just show up because stuff happened. Not the best in terms of integrating the theme, but I think it's an acceptable standard in the genre