Stoupa is great, but like the rest of Greece August will be hot and peak tourist season. If you can delay till September it will be a different resort, not so rushed, more room on the beaches etc
Kalogria beach is gorgeous sand and the sea cobalt blue, if at times a little chilly due to the fresh water springs. If you see some pictures of the bay it has little whirlpools where the water springs are evident.
The town beach is rather shingly, but shares the same excellent view, but backs on to the main road. Early in the season melted snow water enters the bay from the mountains behind via the dry river bed on the main town beach by the supermarket.
There are plenty of followers for this resort, rightly it has a special place amongst us british tourists as it is the way greece used to be.
If you have a morning coffee at the harbour taverna by the fish restaurant, and look back across the bay. Coffee will progress to lunch, the afternoon will slip by ...
That is the magic of Stoupa ....