Not sure about the order, but if I were to make a guess it’d probably have something to do with the alphabetic order of the hashes? No idea.
There’s no such feature in restic that you ask for, AFAIK. But you can of course do multiple restores, each for a subset of the files. You can use the exclude and include arguments to the command, see https://restic.readthedocs.io/en/latest/050_restore.html#restoring-from-a-snapshot for a quick summary.
Either by automating it using some script that uses the ls command, or just manually. Another option is of course to use the mount feature whereby you manually pick which files and folders you restore.