First of all, just like Greekface2 mentioned before, I would totally make time for Thessaloniki, AT LEAST for a day, 2 ideally I would say. Lots of beautiful sights to see, monuments, museums, beautiful waterfront and fantastic cuisine. Despite the fact that Ammouliani is beautiful indeed, it is a pretty small island that offers not that much except from beautiful beaches, and relaxation. A great option if you want to really relax and not do much, not a great option for 4 days if you want to be a bit more active. However, you can also go by ferry to Ouranoupolis and enjoy a day, and also rent a boat and spend another day at Drenia islands, as they are situated very close to Ammouliani. As far as Toroni is concerned, it is also a beautiful area, with not that much to do except from food and the beautiful beach. The same goes for Porto Koufo as well. Amazing beach and food, not that much else to do. The bigger towns/villages of the area are : Neos Marmaras and Nikiti. There are many, many options for places to stay, varying from 5* star to local B&B's. For example, if you choose to stay at Neos Marmaras, you can drive down to Toroni and Porto Koufo in 25 minutes. A 30 minutes drive is to Ormos Panagias to get a ferry to Mt. Athos and also 35 minutes to Vourvourou. It would be good to have a car with you so that you can enjoy as much as possible from this beautiful area. Parthenonas is a beautiful traditional village above Neos Marmaras, towards the hill , which is also not to be missed. There are also B&B's there as well which offer amazing view to the sea, but keep in mind that the village is situated 5-6 km (8-10 minutes drive) from the sea.
Let me know if there is any further question you might have for the area about anything (food, things to do, places to stay, car rental-I'd be happy to help).