*Use standard trim
*Basic 5 inch composite(or component if you're fancy) backup camera.
*Maybe a 3d printed case if you're down to learn fusion 360 (Pretty simple to learn with time). If not, use a prebuilt case and a lot of glue.
*ps2 controller and tact switches(or use at PIC16F microcontroller with ps2plus firmware flashed)
For a beginner, don't set the bars too high. The goal is to finish the project and take everything you learned to build a better portable. Also, make sure you include everything like battery protection (if you intend on using batteries), a charging module and some knowledge of electronics and portablizing stuff in general. I made that mistake building my first portable, and found that custom regs aren't easy to work with.