Hi! Love the idea and the sample clips
It's amazing how much the music can influence the tone of a scene. I like the train & birthday scenes much better now
I agree with Derek, too, about the dream sequence - Harry's dreams were always very important in the books - so what a great idea to open the series with a mysterious dream. If there's anything that could make it better, I would say open the film with the dream sequence, and make it even more mysterious.
In one of the previous samples, I noticed the dream ended with the glowing scar on baby Harry and transitioned to the scar on his forehead in present-day. I think it would make a lot of sense to emphasize/foreshadow his connection to Voldemort's mind via dreams and the scar.
You could start with WB logo, and then transition to a crop of the family portrait from CoS (where she kisses Harry's hand and waves, to show how happy they were), moving on to the scenes from Hagrid's retelling (the hooded figure, the glowing keyhole, the green flash in the upstairs window) mixed with scenes from the Prince's tale that suggest an intruder without giving anything away (the quick shot of the hallway at the top of the stairs, the teddy bear & mobile). Harry never knew what happened to his parents, so remove any clips that explicitly show what happened to them that night.
This will help the scene that comes later, when Hagrid explains how his parents really died. That scene will play as if Harry is recalling his mysterious dream (the clips that don't reveal anything specific) and filling in the blanks with Hagrid's new information (clips of James dead on the stairs, and Voldemort bursting into the room and killing Lily). Basically, it helps the audience stay in Harry's perspective - discovering everything just as he does.
For the audio, you could keep the line where Lily says "Harry you are so loved" and mix it with a sample of Riddle/Voldemort saying something in parseltongue from one of the other movies. This will make the sequence creepier, and will also compliment the scene at the zoo when Harry uses parseltongue to free the snake.
If you wanted to give the scene more context as far as the Dursley's, you could use the parseltongue sample mixed with a clip of the original opening dialogue as a voice-over:
McGonagall: Are the rumors true, Albus?
Dumbledore: I'm afraid so, Professor...
McGonagall: And the boy? Do you think it's safe, leaving him with these people? They really are--
Dumbledore: The only family he has.
End with the clip of him bundled in the basket and Dumbledore placing the letter to Petunia next to him (maybe add the glowing scar effect in this scene, rather than using the closeup) and transition to the glowing scar as he sleeps under the cupboard on Dudley's birthday.
This means the snake/zoo scene will come before Hagrid's letter. Not sure how attached you are to using the letter arrival as your opening scene, but as far as I'm aware, the letters did not arrive until the week of Harry's birthday, July 31st. Dudley's birthday is June 23rd, over a month earlier, so for that reason alone, you might want to reconsider sticking to the original zoo/letter sequencing. Aside from adhering to canon, it would also allow you to use the follow up scenes of the house filling up with letters. This illustrates how much they deprive Harry, and you could experiment with the music to make it seem creepy instead of silly or wonderous.
One other tiny suggestion - in the scene where Petunia is telling Harry about his mom getting "blown up" - rather than cutting away from grown up Petunia to the shot of Lily's hand holding the flower, try cutting away from Harry watching and listening to Petunia, to a shot of young Lily from TPT (and try to match their eyes onscreen). This way you get a more visceral sense of how Petunia
literally sees her sister in Harry's eyes, and why she can't stand him (the next part where young Petunia knocks the flower out of Lily's hand synced up with grown up Petunia saying "I was the only one who saw her for what she really was.. a freak!" is spot on :thumb: )
Anyway, I hope you can see the reasoning behind these suggestions, even if they don't float your boat