Good info above. For this question, my recent experience is this:
You can submit requests to MS anytime, it's never too early. Then, between 10 and 5 days out, call the hotel direct 714.635.2300 and let it go to the operator (which is really front desk staff in the back, I think). Just nicely ask them to verify if your room requests made it over from MS. It's just a double check. We used to call hotel direct for room requests anytime, but I was told GCH underwent a system conversion in the last year+ and now can't see reservations past 10 days out.
I agree with above to submit five or six room numbers. And it never hurts to be nice to at the front desk, or any other time, but I've been told pretty consistently rooms are assigned a couple days before arrival. For the hotel if there are empty rooms, they have some lattitude. But VGC will always be at capacity, of course.
I was surprised by the noise during this past Christmas time on the Pixar Pier side. It was coming from the music stage at an AP event, I think. I don't know if that stage is up and running at Halloween time for the parties. We use a white noise app on our phones to try and smooth it out. Have fun!