New Project: Writer Deck (or Writing Laptop, whatev)

Hi my imaginary reader! Long time no use-this-thing-I'm-paying-for!

My laptop is great, except for when it's not: It's got a low low travel keyboard, which I used to love but I now find uncomfortable after joining the dark side (mech keebs ftw); It's got a fairly powerful i7 from the 8th gen, that produces too much heat and eats away at the battery terribly; It's got a 3000x2000 screen (yup! 3:2), which also uses too much power and is overkill in most cases. Also it's big. Like, it's a 14", it's not humongous, but it does require me to carry it in a separate case.

Thus, the idea: I want a laptop that

uses ARM or other RISC architecture – so, you know, ARM (unless you my imaginary reader want to gift me a handful of daily driving ready RISC-Vs, for which I would be extremely grateful)
has a big ass (bug ass lol) battery
Small footprint. Ideally not any bigger than the
Mechanical keyboard

Okay so, how?

First off, I'm going to base my design around the Raspberry Pi CM5, for no other reason than it being a decently powerful computer with good community support, and me not wanting to mess with DDR5 traces on a PCB since I'm crazy but not an idiot – as in, I know my limits

The design is going to be structured around the HMI (Human-Machine Interface) first and foremost, which means I'm starting with the keyboard and going from there. The keyboard itself replicates layout and dimensions of the one I'm currently using (so, you know, a 68% ANSI) with some tweaks like 4 thumb-keys under the spacebar

Other things: I like the ultrawide 10" screen from Waveshare and it seems to be the perfect size, but anything will be fine as long as it's less than 11cm in height.

Alrighty so, let's play the type-3-fun game of dividing the project into steps and/or objectives, so that I can have an objective measurement of my failure when I abandon it

Design the Keyboard PCB - this part, barring redesigns, is done
Figure out, once and for all, the placement of ports and parts within the frame
Decide on a battery chemistry
Design the mainboard PCB - this daunts me
1. design the Power Management circuitry. This has requirements
  1. Support for USB PD charging of the batteries. Ideally I would like the device to accept >25W, best case would be like 50W
  2. Support for 5V@3A out is necessary, 5V@5A would be welcome
  3. Use-while-Charging seamless support is required
2. Design the breakout of interface pins (they are so very dense) while limiting myself to 2 layers of copper in the PCB
3. Make the board cutout to be compatible with the internals' layout (especially holding space for 18650s or whatever battery I choose)
4. Add all the required off-module circuitry (at least what is needed for this)
5. Put the connectors in their places, route the traces
Design a daughter board that takes in a FFC and converts it to HDMI (because I don't see the point of cluttering the insides with bulky connectors)
Design the case for the assembly (lower half) and figure out thermal management - fans??
Pick a display and design its case
Design a 3dprintable hinge that makes sense

This is really a lot of stuff huh

Well, my dear imaginary reader, I guess stay tuned to see when I give up

Have a wonderful day,

-aki