How can I limit categories to one category or characters of category at front

I would like to set limit characters or one category of categories for instance:

The post shows introduction, featured

I want change it to introduction,… because If I add more than two categories, it will cause posts box look odd at front page.

You can take look at http://test.visualvlogs.net/ and get an idea what I am trying to explain.

However, I do not want limit people choosing categories, just limit characters of category or one category for index.php as front page.

I successfully limited title characters, but I need work on category and tags.

Also, how can I add a plugin or a code to enforce people to choose categories and add title, so people won’t post without title and automatic category to uncategorized.

Thank you for taking a time to read and help in here.