The followup message is sent only to those prospects who accept the connection request but do not message you first.
This message can include examples of your work, your connections, and your extended value proposition.
While the character limit is large, this message should not be. Use your best empathy and think about the liklihood of you reading this message in your inbox. Generally, an open-ended question is the best way to progress them down the sales funnel.
Definitely include a link, phone number, email address, or all of the above here. This CTA will attract some leads even if they don't follow-up on LinkedIn itself.
*You can use name and company names here, just wrap them in some brackets.