We stayed at Vassia's house for two weeks on our first stay to Sifnos. The pictures do not do the house justice - it's all arranged an inner courtyard with some beautiful plants. The bedrooms are off that which makes it feel like an old Roman villa. The rooms have great charm, with lots of antiques and lovely furniture but designed to be very practical (a very well equipped kitchen and an almost too-strong shower!). The patio at the back is lovely in the evening as the sun sets across the hills in the distance.
The house itself is a four minute walk to any car park - but that's standard across all of Sifnos where most of the towns are pedestrianised. It was nice in the evening to wander into Apolonia (a five min walk) to get a pizza and then just head on back to the house. The local grocery shop does delivery which we didn't end up using but would be helpful if you're slightly older or with kids, in case you're lugging back big bags of shopping.
Overall, Sifnos is beautiful with terrific food and lovely beaches. We most loved the more wild ones in the north of the island. Vassia's place was the perfect base for our time there - we shall be back!