Using a pi4/cm4 as the heart of a DAP, questions about some parts of the pi part of it

The basic project scope of this is to make a DAP (digital audio player), where I have a power bank of some sort that powers a cm4 and a DAC/amp for semi-portable HiFi audio. All of my questions will be posted outside of this main post so they can be individually replied to, anything past this can be considered unnecessary but gives some insight into why I have the questions I do. Background I like good audio stuff, I don't like the way a lot of products are designed. Most DAPs are made to be used like a phone but are pretty huge and run on versions of android that often lose support from any of the decent streaming services just a year or two after release and are a pain to take apart to replace the battery when that's a problem. Most DAC/amps either have the same battery issue; are made to draw power from the host device over USB (rarely pd), leading them to cause additional battery drain and have relatively low power output; or are made to be used as desktop units and throw any concern of size out the window. My experience with RPI is pretty limited but I have done some involved electronics projects before, just based around different control methods. Plan My solution to this is to have a battery pack, most likely going to run off of 21700s and incorporate the power management and safe shutoff stuff in it, that powers a raspberry pi with external storage like a naspi cm4 type deal, into a portable DAC/amp that's had it's battery removed to run solely on external power also from the bank as the pi doesn't want to feed very much power. This stack while it would be very high quality output runs into an issue similar to DAPs here, it's not small. So I want to make the screen element to control what's playing separate from the rest of the audio stack so the stack can just be in a backpack or something, ideally wirelessly (but not using Internet protocols like ssh to avoid needing a router), to control what's playing and all the navigation.

With something like the naspi cm4 in the picture for part 1 it says the power input USBC port is also an otg cable, does that mean it can be used for data/commands as well to be able to have the battery pack include the power management circuit that sends the shutdown command when it's at low power? Product link I'm talking about: https://geekworm.com/products/naspi-cm4-m2?variant=45379738272057

With the same product as above are the gpio expressed through the USB ports? I don't know where it has them going but when using an external DAC/amp it is always better for the media player volume to be maxed and the volume to be adjusted at the amp stage. The one I'm planning to use uses a potentiometer to do this, would I be able to artificially emulate that through the outputs of this board so I can control it without touching the actual potentiometer knob or would I have to keep the physical one accessible?

Is there a good way to run a touchscreen display (I'm fine with it being an old phone/tablet or just a display with a smaller battery attached whichever would work better) wirelessly to the pi without them having to be on a network? It doesn't need to have a range of more than ~8 feet or be very high resolution as it would basically just have VLC (or similar) open to skip through music or select another track. I know they make "wireless HDMI cables" but I don't know if that would work for the touchscreen capabilities or if there's a better (non-networked) way to do this.

I currently have a cm4 8gb and 4b 8gb but since this wouldn't be doing a lot of processing and is just sending the files digitally to the DAC and won't be used for videos, would it be better to use a lower speced version for thermal management or battery life? Would the difference be noticeable if they run the exact same load?

Bump