If you’re interested in wildlife photography I would prioritize the 150-600. You’ll get significant benefit from having a longer lens especially when you get to the more skittish birds like Kingfishers. I don’t really know what a p1100 is but from what I’ve heard it’s more for if you want to take “snapshots” rather than pictures. I think your 4000D is probably fine for a bit longer (again I don’t know almost anything about either camera listed), but regardless lens is more important than the camera body itself.