I have solved the problem, sort of, but not with functions.php.
My WP is in Japanese, so it has a plugin to fix double bite word codes called “WP Multibyte patch”.
There are configs in that lets me adjust the excerpt length.
“Read more” still does not appear when I place page breaks in the posts, but I am satisfied with this setting, so the first problem I have is no longer a problem.
If the theme creator could help in the page break and “read more” settings, it would be greatly appreciated.