Santorini and Mykonos are crazy expensive have that in mind
I would do 3 days in Santorini and 4 in Mykonos
Paros and Naxos is Kite surfing and wind surfing paradise so if you are in to sports stay longer then 3 days in Naxos
The best place to stay in Paros is Naousa, great food and bars, a lovely place!
Rent a car in Naxos and go around, the south part of the island is beautiful also the small villages inland are very pretty
make sure to visit Antiparos, there is a ferry every 30 minutes crossing from paros
Folegandros near Santorini is the new big thing in Cyclades, not my thing but a lot of people seems to love it
Paros and Naxos are both worth to rent a car and drive around
have fun