Paros isn't that close to Athens. Maybe your thinking of Poros. There's a lot of islands.
Kea is very nice, same for Kithnos, Sifnos, etc. If you want to go to Hydra then I'd suggest anchoring
outside of the harbor as it's a true cluster f#$3 of boats. Awesome island though.
We were in the Ionian's this August and it was pretty packed. If you tried to come into a harbor after 3:00pm, it would be tough to get a berth. But that ended up ok for us as we searched out the farther away spots and they turned out better. So many crossed anchors it was crazy. In general though, I'd still suggest the Ionians or the Sporades. I think they are prettier.