Okay, the books I do have (besides the Player's Guide, the Dungeon Master's Guide, and the Monster Manual) are Xanathar's Guide to Everything, Modenkainen's Tome of Foes, the Sword Coast Adventurer's Guide, and Volo's Guide to Monsters. So if you want to use some option from one of those books, feel free to do so! Just be sure to mark where you are getting your options.
You don't have to completely post everything about your characters right now, but I'd like to know your character's class, race, and basic outline will be like so that I will begin constructing your kingdom with you. Also, if you want to have a say in what your character's kingdom is like, let me know.
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Okay, I have the idea for the starting adventure.
I'd imagine that, as royal heirs, the PCs would have the kind of boredom rich kids tend to get. They've grown up hearing tales of how their parents were these great heroes, and they've even gotten to see them in action, and they want some of that excitement. But more than that, they want to prove themselves worthy. So they decide to meet together in a small town to do the medieval equivalent of slumming. They get to know some of the locals, beat up some gang members, get to meet some of the quirky characters, etc. Whatever your characters come up with, they'll try to get done. Then, at night, a monster attack occurs, the town's leaders are killed, and the town itself is devastated. Now, the PCs must show their leadership chops by helping the surviving townsfolk. In doing so, they prove themselves to be worthy royal heirs and their legends truly begin.
What do you guys think?