I informed you that
In 1481, a visitor indicates a large synagogue was serving the community. Rabbinical responsa on issues of observance of laws of agriculture in the 15th century are recorded. A Reb Meshulam of Volterra visited Gaza in 1395-96 and reported houses and fields of Jews and as they were well developed, it is surmisea,
If you searched here, you'd notice, I hope, a gap between 1870 to 1929 (as also here; and also at the Wikipedia entry).
I have in my possession a Hebrew book entitled: 40 שנות ישוב יהודי בעזה באר-שבע והקמת חוות רוחמה. It's by Mordechai Elkayam and was published at the end of 1994. It contains the following relevent information regarding the presence of Jews in Gaza after 1860 but also other details I didn't find in the above (such as in 1170, Ovadia Bartanura noted 70 Jewish families in Gaza and 2 Samaritans and that was verified by visits of Rabbi Shlomo of Praga and Meshulam of Voltira but here in Hebrew).
In 1882, the Chovevei Tzion branch of Jaffa decided to expand Jewish residency and especially in Arab demographic areas such as Gaza, Lydda and Shchem and the first nucleus was founded in 1886. The income would be based on barley export and a medicinal plant, Schrad. A jerry was constructed in 1910. There was a break between 1916-1918 due to the war.
The founding meeting took place during the Succot holiday 1886. Nissim Elkayam and Avraham Haim Chelouche rented large houses in Gaza city.
Another group went south and rented houses on Harawt El-Zeitun. Five months it took for the first families to arrange everything and arrive to settle in until Pesach. They all possessed foreign citizenship, English, Spanish and French, which allowed them the privileges of which other Jews did not benefit. And four (!) synagogues were eventually established divided by the families. By 1890, 30 families were in Gaza.
The book of over 400 pages with pictures and notes and documents is a fascinating read. For example, one month before the May 1921 riots, Sheikh Haj Said El-Husseini informed Haham Nissim that extremists were demanding of him permission (fatwa) to strike out at the Jews in the city. Nevertheless, all left for the few weeks until the Arab rage quieted except for Eliezer and Tzila Margolin and family who remianed in the city, trusting the Sheikh's assurances that they would be protected.
In 1929, on the Thursday before Friday when the outbreak of the violent riots in Jerusalem "spontaneously" occured, a Jewish policeman of Indian origin, approached Nissim Elkayam and Eliezer Margolin and informed them that all the 100 or so Jews residing in the town were to be collected and brought to the Yaffe Hotel. Even the Jewish wives of two police officers, Partrize (phonetic) and Starsky, were brought over. Arabs beseiged the hotel and one broke in but supjuric acid was thrown at him by Dr. Jeker. After Shabbat, all were transported to the train station under the guard of the Sheikh and police and made their way to Lydda and Tel Aviv.
In 1972, when one of the Sheikh's sons, by then a PLO terrorist was hiding in the basement of Radja El-Shawa, Moshe Elkayam convinced Moshe Dayan not to blow up the house in recognition of the father's efforts to protect the Jews of Gaza in 1929.