Even though that would be impressive, creating a CPU from scratch (and then loading it with a program) would take more than what most would consider worth it.
You would need the CPU, some sort of memory, interpreter logic, communications bus to go between the three, and something to do with all of that.
Something that would have a text interface would be virtually insurmountable, because you would need again another processor with memory (to hold the video bitmap, and the font bitmap).
Estimate for a 3-bit computer, 3 bit addresses for 3 bit characters (really?) I would estimate approximately 4500 placed redstone, 3200 pistons, 2000 repeaters, 40 glowstone (for indicator/output), 12 levers, 2 pushbuttons.
But if you do manage to do it, You should be able to land a job in just about any electrical engineering job
Gook luck!