Don't tell anyone but that yuri manga about the nations based on 4 elements has 4 princesses.
There isn't much on the others besides Snake Princess, but they're the biggest example of "Kamejiro has a lot of plans it's going to take us painfully long to see." Some details might have changed, though this is fairly recent material on them and Snake Princess and Fire Princess seem about locked in. Earth Princess always got the least exposure and changed around a lot, but Kamejiro seems to like making her extra bullyable and handing her a gun.
The love interests are even less known, but Monk is meant to be a commoner who found her way into wealth while Snake Princess is a noble whose family has been disgraced. Assassin is meant to be mute and emotionless on the surface, but she and Fire Princess are legit married. Can't tell you anything about Hunter other than she looks like an actual shoot-first-ask-questions-later psycho to contrast her dorky partner.
Each princess also uses a different title in Japanese. Wind is 皇女, Fire is 王女, Water is just 姫 or used to be 姫御子, and Earth is お嬢様 - the only one who isn't a literal princess. It might say a bit about their cultures.
Also Sara does officially graduate from nun to priest, which should be interesting in the new version where the royal priests look down on her.