Hi Dave,
We were at Arillas in June and we too enjoy a good walk.
You can walk around the whole of Arillas, it is like walking around the block I measured the distance and 2.6 kilometres (or near that)
You can walk to San Stefanos via the cliff walk, this is quite a climb but really worth the view, alternatively you can walk via the road which isn't so bad.
The walk to St Georges is about 3 miles but again rather a climb, but it is nice to get there and sit in a taverna by the beach enjoying an Amstel!!
Have a wonderful time, I'm really jealous, Arillas is one of the best resort on Corfu!!