Need Some Help If Anyone is Able/Willing

Hey guys, so I was kinda hoping youguys could help me out. I had a story idea recently which crossed over Harry Potter and Persona 5. Essentially, Harry stumbles upon a world, known as the Metaverse, that allows him to see the world through the cognition and distorted desires of an individual. While there he learns that Dumbledore isn't as light as he presents himself to be, and awakens to the power of Persona to stop him. My problem is coming up with a good starting point in the Harry Potter timeline, and assembling a team to join Harry on his expoditions into the Metaverse. Is there any advice you guys can give me?

Oh, and if I like how this idea turns out when I write it, I'll post it here for review.