Am I too late?
1) Favorite Grand Duchess -- Olga Nicholaievna Romanova.
2) Favorite estate -- Any place they stayed while at the Crimea Peninsula, of course. Fresh air, excellent climate, and the Black Sea. :-D Finland skerries are not that bad, of course.
3) Favorite Tiara -- the one Empress Alexandra wore during 1911 photo-shoot.