I wanted to be able to run a dedicated graphics card, which greatly added to the size of the machine. Also, decided on mounting a stap to sling over the back instead of a carry handle, for mobility. Minimum laptop size display for usability, also could recycle outdated laptop. Finally, so that it can double as a tv pc, mounted a detachable wireless keyboard/trackpad combo for remote control.

Used a busted keyboard from ebay as the main body for structural integrity. Bonus - metal back provides strength, and since its screwed on, would be able to easily replacement/upgrade.

Considered and rejected:

multiple graphics cards - weight and power requirements

adding a mechanical keyboard - size

touchscreen monitor - expense

dual monitors - expense, weight, room

Full size atx motherboard - would fit, opted for mini itx, still has the 1 pci express x16 slot for a graphics card

Batteries for mobile use - ones that could power a full desktop build for any sufficient amount of time way too heavy!