Excerpt length decision

What should I take into account when limiting the text visible on a listing? I'm using a list layout with images on the left side, a title, a meta line and the excerpt, And I've wondering if there are any best practices like:

  • limiting the excerpt to full sentences only without breaking the sentences
  • limiting the text to fill n lines
  • limiting to words and add three dots and read more link afterwards
  • limiting the words and using justified text alignment ...

What do you think?