Hey Buddy,
You can just shoot in 4k60fps and that footage would be crisp and perfect. ProRes is basically for people who wish to tweak the details in the video like improving highlights or white balance change, etc. I would say it is not that useful and if your videos are recorded in a well-lit room you are totally fine to use the 4k60fps option. For storage, you can use an HDD or SSD, and store it safely, and let people know where to find it and it is best not to encrypt or password-protect the storage. Sometimes shit happens with password protection and we don't want that now. Multiple copies are appreciated.
You are doing a great job as a dad and I am sure your daughter will cherish all the effort you are putting in, to make her happy. I wish you all the warmth you can get.
But why does he need a smartphone? Is it because his education demands it or all his friends have one and he wants it?
It is good to keep one updated in terms of technology and content but having a smartphone at such a young age is probably not a good idea. But if he insists, 13 or 14 series would do. Personally, he can make use of the iPad or a Galaxy Tab for both studying and movies or games. I remember sharing my phone with my brother when I was 16. It was a Sony K310i, oh man, the fun we had using that phone, having an IR blaster to transfer mp3 files haha.