No worries, you'll really only need to learn a little about electronics to use our screens.
Both the screens I mentioned will in fact remember the number entered with the start screen function and interface to a keypad. As long as power is supplied to the display, it will show a number, you'll only need to use that start screen function if power has to be removed.
I see you are looking for a USB connection to your PC, for that I'd recommend the LK202-25 with USB, something like the LK202-25-USB-FB
would work well. For a keypad, you can use our 4x4 unit
or your own passive style device.
Of course in either case you will need a host controller or computer to run the display. When keys are pressed the display will send them to the host which will then write them to the display. The host can also tell the display to save the characters as a start up screen if they need to be remembered.
If you have any further questions, just post them.