South Goa has a lot of options, Palolem, Agonda stretch if you want extreme south. You can do water sports in Palolem. Beach shacks have good food options too though bit expensive. My recommendation would be restaurants like starlight, amarela, seamen's, Joe's river cove in Assolna for best seafood in South.
If you are planning to South goa then stay at palolam beach this is my favourite place to stay.
If you want luxury stay then cavelossim is best for beach resorts.
Palolam, agonda and morjim beach is best for water spots activities.
Then must visit places are Cabo de rama best for cafe and views , kakolam beach with 2 waterfalls , Butterfly beach away from croud.