iphone x camera files sizes I'm going to buy iPhone X and I wonder which size will be most appropriate, 64GB or 256GB.

I'm not a big user of apps, taking pictures or video but because my iPhone 5S 16 gb is full right now I am afraid iPhone X will fill up in the years ahead. I'm using iCloud storage to optimize storage on iPhone so all my photos and videos are on iCloud.
For now I would like to keep all my files on the device.

How large are the pictures and videos on iPhone X?
For example how much space will be used by a 1 minute video?
If you’re not a heavy user, 64GB is more than enough for what you need. Here is the size of videos in different resolution

1 minute 1080p at 30fps will be 60MB
1 minute 1080p at 60fps will be 90MB
1 minute 4K at 30fps will be 170MB
1 minute 4K at 60fps will be 400MB
(Approximately)
More resolution can be seen in Settings -> Camera -> Record Video

One high quality photo from my phone is a little more than 20MB.

Unless you’re filming at 4K60 all the time (for your job or something), and you don’t use big apps, 64GB is good enough for you. Otherwise go for the 256.