Thanks for the insight into your game.
I'll definitely revisit this game as time passes on! Around every couple of months, or whenever I see you've implemented a major patch. I'll be writing suggestions again and looking out for bugs when that time comes.
I have to admit it's pretty inspiring to see a solo game developer make a pretty ambitious game, I'm glad to see you work fast and seem to be quite passionate and consistent. I completely understand that you don't want to monetize, because then you have to start making the game based on your consumers preferences and not your own.
Speed up button: I like the idea of combat being sped up when your agility is higher, I think this is the best option for making sure the player won't be spending too much time fighting weaker opponents.
Weapon parts crafting: I had a look at the anvil in the Riverstone Smith, and there is the ability to craft weapon parts, I missed that.
Helmets: I'm not entirely sure what the best option is either, perhaps the option you mentioned, or give the player the ability to toggle the helmet on/off whenever they want? I don't know if that is possible with just a button press in RPGMaker.
Fallout style limb system: If you were to add something like this, you could definitely make some 'gimmick' enemies that have high resistance to damage or has access to a powerful ability until you deplete the limbs health. For example: fighting a cyborg that has an inbuilt cannon inside their arm, they would deal tons of AOE damage until the cyborg's arm reaches 0 health.
I also want to mention Suong is the best character followed by Billy, then Helena. Helena's fire spell is super powerful with the [in flames] damage over time effect.