We did Northern Greece and I'd suggest it has everything you want.
Started in Thessaloniki which is fab, then picked up a hire car. Would not recommend driving in Thessaloniki but everywhere else was fine. There has been a lot of EU money spent on roads and bridges following the Greek financial crisis and so driving was surprisingly easy.
Then road trip:
Tomb of Philip of Macedon in Vergina, absolute must do.
Historic sites at Dion and Pella - lots of original sites of myths, next to Mount Olympus
Museum at Larissa - really well done on the history of ancient Greece and absolutely nobody there
Across country to the monasteries at Meteora (you definitely need to be energetic for this!)
Into the mountains for Metsovo - warning, drive is 'scenic' by which I mean tortuous road up side of a cliff. We didn't get to see the view as we did the whole thing in thick fog, when the fog lifted we felt a bit sick.
Then back to Thessaloniki via the waterfall at Edessa
You are also very much in the footsteps of St Paul if this interests you, we came across a few American religious tour groups who were retracing his journeys.
Lots of opportunity for beach from Thessaloniki and boat trips to Mount Athos.
Didn't feel we had missed out by not going to Athens (DH has been before) but have earmarked it for another holiday.
There was so much history - ancient Greece, myths, Ottomans, early Christianity, it was just great. And the food was amazing.