Sampling voice and send it over cable, which A-D converter is best for it?
I know that I can send the voice as an analog signal directly through the cable ...


Since you're "starting from zero", I would recommend doing this as a first project. This will teach you a lot about power supplies, handling microphone and speaker signals, and some of the logistical issues associated with the overall application.

You can always "upgrade" to digital later, as a follow-on project, reusing much of what you've already got, including the cable. That will bring a whole additional set of issues, by which time, you'll have more experience to deal with them.