Hey, I am a programmer and got a pretty nice idea today which I would like to have done if this is possible.
I thought of having a really small component containing cpu/ram/ssd soldered like in a laptop, that you will be able to plug in the "peripheral" part which contains the screen/mouse/buttons/others.
Basically this is a mini pc that you can plug everywhere, so you could have a device small as a phone, a tablet or a tv and still get the same storage.
Like I said I am a programmer so I should be able to manage the software part even if I had to make my own OS, but I know close to nothing hardware side. I first thought of using a raspberry but I would like to have a more powerful cpu/gpu, same for storage/ram size. So I believe that I need to use laptop parts or even a whole motherboard, for learning purpose I would like to build my own but I feel like buying those parts isn't available for consumers (maybe on ebay?)
Since having windows or any other current OS isn't my priority I could even use a ARM based cpu architecture if I have a way to buy one of them (like a modern smartphone processor) but it seems impossible.
Basically, how can a get parts for what I want to achieve? I know that this is really hard and probably out of my knowledge but I would like to learn eventually.