1) In some communities the custom is to recite the complete Hallel with a bracha on the first night of Pesach in Israel and the first two nights outside of Israel. This is the custom of those that pray Nusach Eidut Mizrach, Nusach Sefard, and Nusach Hagra. (S.A. 487:4 and M.B. 9)

2) Harav Shmuel Kamanetzky shlit”a explains that even those that recite Hallel in shul on the Seder nights only do so with a minyan. Therefore, if one who davens Nusach Sefard (which recite Hallel) and he did not go to Shul on the Seder night, he should not recite Hallel when he is davening alone at home. (Koveitz Halachos Pesach page 196) However, Harav Ovadia Yosef zt”l (Yechava Daas 5:34) proves that many achronim (including the Chida) maintain that one can recite the Hallel without a minyan.

3) There would be a similar question regarding whether women should recite Hallel at home before beginning the Seder. According to Harav Ovadia Yosef zt”l (Yechava Daas 5:34) they must recite the full Hallel since they are included in the miracle of leaving Egypt. However, according to Harav Shmuel Kamanetzky shlit”a (Koveitz Halachos Pesach page 196) they would not say it since one only recites it in Shul and women generally do not go to shul on the night of the Seder.

4)  If one is in a shul where they do not recite Hallel and his personal custom is to recite Hallel, he may recite Hallel quietly in the shul. (Chida Birkei Yosef 487:8) However, according to Harav Shmuel Kamanetzky shlit”a (Koveitz Halachos Pesach page 196) it would seem that they should not recite Hallel since they are not reciting it together with the minyan and Harav Shmuel holds that one only recites Hallel in shul on Pesach night with the minyan.

5) What is the halacha if someone’s personal minhag is not to recite the Hallel, but he happens to be in a place where the Hallel is recited?  What should he do then? Rav Moshe Feinstein zt”l (Igros Moshe OC Vol. II #94) writes that if someone finds himself in a shul that recites Hallel it is preferable to recite the Hallel and not act differently so as to avoid Machlokes. He adds that although, ideally he should do so without a blessing, if it will be readily apparent that he is not reciting a blessing, then he should even recite a blessing rather than appear to act differently. Rav Shmuel Kamenetsky shlit”a (Koveitz Halachos Pesach page 197), however, is of the opinion that it is preferable to leave the shul earlier rather than recite the Hallel earlier. Rav Kamenetsky advises that it is preferable to sneak out of shul undetected.  If this is not possible, he advises to recite Tehillim instead – also in a manner that is not detected.