138:4 On the night of Shemini Atzeres, one should wait until night to make kiddush. Shehechiyanu is recited in kiddush because Shemini Atzeres is a festival in its own right. One does not recite the bracha “leishev basuccah” because we say “yom hashemini, chag ha’atzeres hazeh” (“the eighth day, this holiday of assembly”) in our prayers and in kiddush. (There are some variant versions of this phrase – Mishnah Brurah 668:3 – but all express the same idea.) To also say “leishev basuccah” (which suggests that it is still Succos) would be a contradiction.
138:5 On the night of Shemini Atzeres, and the entire day, we eat in the succah without reciting the bracha “leishev basuccah,” as we discussed above. After we finish, we recite “Yehi ratzon….” Some are lenient when it comes to sleeping in the succah and this is the accepted practice, though it would be more appropriate for one to be strict in this matter.