ラブライブ三昧 is a special music program of NHK FM 今日は一日○○三昧, which plays music of a theme for the entire afternoon and evening.
みどりの日 means Greenery Day, a national holiday in Japan.
タイトルホルダー is the transliteration of Titleholder, a Japanese Thoroughbred racehorse.
虹ヶ咲 is short for ラブライブ！虹ヶ咲学園スクールアイドル同好会, or Love Live! Nijigasaki High School Idol Club.
ゴールデンウィーク means Golden Week