Hi, Stephen! Welcome to planDisney.
Congratulations in advance! Proposing at
Cinderella Castle is such a magical way to pop the question, and it sounds like you're really putting thought into capturing the moment perfectly. Disney has a ton of ways to make proposals special, from reserved spots to
Disney PhotoPass photographers, and it's brilliant that you already have
Memory Maker to cover the photo piece. I totally get wanting a video too. There's something about seeing the moment play out in motion that photos just can't capture. Planning ahead is key so you can focus on your girlfriend (soon to be fiancée) without worrying about missing the moment.
Whether a Cast Member can record video on your phone is up to their discretion. There's no official policy saying they can't, but if protocols change, they would politely let you know. Most of the time, if they're not busy with another task, they're happy to help, so it's definitely worth asking once you get there. Some Guests also set up their own phones on a tripod in advance if it's allowed in the area, just to make sure the proposal is captured.
Pro tip: Plan your proposal for a time when the area isn't too crowded, like early morning or after fireworks viewing, so you'll have a clean background and fewer distractions. If you're hoping for video, you could even scope out a spot in advance to safely prop your phone for recording while you get down on one knee. But just remember, the most important thing is the moment itself, rather than capturing it.
Enjoy your happily ever after moment, Stephen.
Mike