I just picked up John Collins and Gregory Sterling on Hellenism in the Land of Israel (edited volume). Articles by Hengel, van der Horst and Vanderkam are helpful. Not sure we have any specifics on first century Jewish authors writing in Greek from Galilee beyond Josephus (a question Bart Ehrman asked me in our radio debate).
What we have are 3 % mss at Qumran, significant Greek remains among ossuaries and some Greek collections (e.g. in Frey, 315 of 530 inscriptions are in Greek). Collins notes three writers of Greek in the Holy Land in the Maccabean period: Jason of Cyrene, Eupolemus, and an anonymous Samaritan. Murabba'at and Babatha archive 55% of 609 papyri in Greek. Romans issued their decrees in Greek. Van der Horst says Roman Palestine is largely bilingual. One sentence from that article: "The burden of proof is on the shoulders of scholars who want to maintain that Greek was not the lingua franca of many Palestinian Jews in Hellenistic-Roman-Byzantine period, in view of the fact that more than 50 percent, maybe even 65 percent, of public inscriptions in 'the language of Japheth'." (p. 166). He does also note use and understanding did vary according to locality, period, social status, educational background, occasion and mobility.
I would take it the more mobility, the more exposure is likely. Van der Horst also notes that we know a small percentage of people who lived then in what we have (a reminder that our evidence is fragmentary). But what we do have from a variety of locations shows the pattern.