At the bottom of each post I need to either:
- Offer a link to the next post (if the next post is published); or
- Display the title of the next post with the date it will be published (if it's a future post)
Add these two where you want them to display within your single.php file. It will make the title of the post a link.
EDIT: Sorry I missed the second part of your question about future posts. Here's what I would probably do. It's not tested, but will give you an idea.