Glad that you liked it! The nuke definitely helps with "cleaning up" :D
You are right an audio cue probably wouldn't be bad for the nuke charging. You can always stop charging and move instead and start charging again later. As long as you don't let too much time pass you won't loose the nuke charge. Bullet damage should be same for all projectiles, but the later enemies especially the "proximity" ones have very tight fire pattern almost like a shotgun so you might have gotten hit multiple times or perhaps lost health earlier already.
Awesome to hear, thank you for your long feedback :)