Good plan; two days to see it all. I've been to both. If you go off season, you would be more squeezed for time in fewer hours of daylight. If you go in summer, you could see more; but it would be a long day in the heat, so take water. Also, there are lots of videos on YouTube and elsewhere to pre-view the sites, so your tour would be more comprehensible once you get there.
I went more or less blindly the first time, but it was a long time ago before a lot of the excavations and restorations were done. The second time 15 years later revealed a lot more; and that, too, was many years ago, so by now there's really a lot to see.
Also, the Archaeological Museum of Napoli is outstanding!
That does it, I’m goin’.
I wonder if they have pizza in Naples? ;^)