Formatting Post Length and Inserting a Line After

I am relatively new to wordpress. I know enough about html to edit basic things, but adding my own code is difficult. I am working on a new template for a business wordpress. I want to create a general rule for the amount of lines shown from a post before “read more” appears.I also want to add a simple line between each post in order for our homepage and category pages to look more put together. Is there a simple way to handle these two things?

I want to gain as much WordPress knowledge during this project so anything would be helpful.