About your safety

The overall security was good. Be careful with pickpockets in touristic places and in the metro, as in many big European cities.
As a man, Athens is a very safe city. I can even say that I felt safer in Athens than in Lille. Of course, as in all European cities, beware of pickpockets on buses and metros.
You shouldn't walk around alone outside in the center of Athens.
Like in every capital city, you need to stay vigilant to avoid pickpockets.