I know that there is a custom to get an Aliyah and give kiddush the Shabbat preceding a yaharzeit. Does this apply to the first yarhzeit as well, when the person is still in availus-assuming the deceased is a parent?

ב"ה Shalom,, The classic Minhag of Shabbat before the yahrtzeit, which is mentioned in Sefarim of Halacha , is to read the Haftorah. There are different customs in regard an Avel in the first year if he should be can be Chazzan for the Tefillot on the Shabbat before the Yartzeit. Each bet Knesset should follow their minhag. If the local practice is to give a Kiddush on the Shabbat before the Yahrtzeit, you may do so. The purpose of the kiddush is obviously not to celebrate but that people say Berachot in honor of the neshama of the deceased, therefore the greatest zechut for the deceased would be to have some Divrei Torah said at the Kiddush. All the best and Besorot tovot