Celso we stayed and surfed with Nusa Island Retreat. great place. Where did you stay when you have been there?
Yep Dec-Mar is best for surfing the area. In winter it is the scuba diving months and mostly flat.
Like I said you'll have to check out the boat options, nusa doesn't really have a dedicated fishing boat, just long boats for surf transfers and some trolling the immediate area if the surfs not happening.
Cheers Tony