Stelios’ apartment was perfectly located between downtown Thessaloniki (plateia Aristotelous) and the upper town (Ano Poli) but be aware that the street Agia Sophia is uphill so it is easier to access by cab from Plateia Aristotelous even if it’s only a 12 min walk, especially with luggage. The apartment is also on the 4th floor and does not have an elevator.
You can really walk to all main attractions, as highlighted in Stelios’ little guides of the neighborhood’s main attractions which we made very good use of. We also tried the restaurant Kanoula that Stelios recommends in his guide, which was very good (small taverna 7 min walk from the apartment). Aigli is also worth the 5 min walk for their excellent cocktails (approx 9€/cocktail, open until 3 am).
Wifi was working perfectly. We enjoyed a lot the terrasse which makes the apartment (which was slightly tighter than expected even for two) bigger. Communication by phone was good with Stelios (he does not live on premises). Check in and out was easy with the lockbox situated in front of the apartment.
We made use of the washing machine but be aware that it does not seem to have a spin at the end so the clothes were a bit wet, this was not a big problem in the summer but you may want to plan laundry in advance (a day before leaving) to ensure that the clothes have enough time to dry on the terrasse.