crf is quality, smaller number = bigger files. bigger number = shittier movie quality. 22 is basically the happy medium between quality and size for me. This will convert, from the source file, the first video stream to x265, all audio streams to 320kbps aac, and will also copy all the subtitles in the file as well.
you can do other fancy stuff like scaling but if you're just looking for a good-enough backup of your physical disk, this is a great start.