I enjoyed my stay at Sofia's. She was very helpful, communicative, and accommodating. For any non-Europeans, I recommend downloading the Moovit app -- this is how I was able to navigate the bus system with ease. Sophia was also quite helpful when I asked about bus connections and offered advice on how to get to a beach (I was amazed at the speed of Thessaloniki's bus system).
The apartment's location was just a little bit outside of the city center. It was easy to seek out people and noise during the day and a refreshing break to retreat to the more laid back, quieter area at night. The bus is just a few blocks from the apartment and can drop you off at the city center in 15 minutes. Fantastic views from the apartment and wonderful walking and running paths along the sea.
One last suggestion: try to make it up to Ano Poli for a view of the sunset on one of the days you're visiting.
Thanks again, Sofia!