You should give a look at Long live the Queen. From your list, the main downside is that you don't play a party of characters, but otherwise:
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-I am looking for an RPG. It can be an action RPG or a Strategy RPG or any kind of RPG.
You can train in various aspects (combat, intellect, strategy, manners and etiquette - remember, you are a princess -, magic...) and how you train affects how the story unfolds.
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-A decent sized cast of characters. Not a game with like 3 characters. I'd say at least 5, although the more the better
You only play one character, but the cast around really has its importance. Depending on how you play, you'll see some more than the others and learn different things.
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-Some good female characters
Plenty of them.
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-An easy enough game or at least one with a difficulty setting
Surviving is fairly easy (though you might die in your first playthrough, but die and learn is how it works. There are achievements for dying the different ways you can die, in fact.). Getting all the endings will require planning because story branches. Since it uses the visual novel format, the difficulty isn't skill based, it's managing yourself right so you don't die from, say, the first duel thrown at your face but have the skills to overcome it one way or another.
Optional:
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-I prefer anime style art in the game, but that's not a need
Check.
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-Some humour in a game would be nice
Check. It's definitely full of humour.
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-Dating sims are always a plus
Who and how you date him/her affects the story. Depending on how you play, the same character may be your lover or your worst enemy.
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-If the majority cast was female or even the main protagonist, that would be great
You're the princess in this game :D