I don't currently solder, but my dad has a soldering iron and I'm familiar enough I could pick it back up and practice a few times for this.
Phone charger would be an option, I was just intending on the PC to save power strip ports.
I'm not really sure about the buzzer. I guess it's less about the pitch and more about the volume for me, I just need it loud enough in case I'm in another room. I guess high pitched probably works better for that I'd imagine, but IDK