/diy/ - Do It Yourself

I'm looking at building a handheld UMPC/oscilliscope out of a raspi 4 and an espotek labrador, but aside from a knowledge of automotive electronics I'm out of my depth.
My goals are:
>battery powered, with the ability for the OS to see the battery charge capacity
>salvaged netbook/custom keyboard that has a small form factor
>trackpad or mini trackball, maybe thumbstick
>wifi and 4g connectivity
>screen with adjustable brightness

How would I go about making this work?
I doubt the keyboard and trackpad will be USB compatible, will I be able to run them off the GPIO pins? Is there some kind of battery controller available that gives a digital output of the state of charge of the batteries?