Iera Odos is very close to Monastiraki and Theisio. You can go there on foot. Be prepared to return by taxi if you stay out late, cause walking towards Iera Odos at night can feel a bit unsafe, although it shouldn't be. It's mostly psychological cause not many folks are walking in that area. Taxi is 3.50€ at the time of writing from Theisio, and it's super easy to catch one.
The apartment is great. Very big, the bathroom very clean, the towels smell good, and the view to Acropolis is beautiful. The building is very very old, and smells because of the moisture but once you enter the apartment, you enter a different world.
You will probably never see Toni, but that wasn't a problem. His assistants were very helpful and polite. They even called us while on the road to make sure there is someone there waiting for us to arrive.
If you own a car, be prepared to park it across the street in the Metro Parking if you want to be safe. There's plenty of room to park it out in an alley, but it may not be 100% safe. I had folks telling me breaking windows is rare and others telling me it's not so rare. I wanted to avoid thinking about it so I paid 12€ a day to park my car in the closed Metro Parking.
Other than that everything is great! The only problem with the apartment is the refrigerator door. It doesn't open easily because the enclosing cabinet stands in the way. This is of course a minor issue, but I like paying attention to details.
Air conditioning worked great, plenty of hot water although you have to manually turn on the water heater, wait for 20-40 minutes, and then turn it off and have your bath. We didn't cook, but the place looked like it had every utensil you might need.
Overall, I would stay again in the area.