Changing the <title> can only be done when you link K2 content to some menu item. You can't have a different title out-of-the-box for content that is not linked to menu items.

On the other hand, if you want such control, it's pretty easy to make your own field (through K2's extra fields) and have that field replace the default <title> tag with your own.

E.g., at the very top of item.php and after the "defined('_JEXEC') or die;" line add this:
Make sure the change is done in an override for item.php inside your template (more info here: getk2.org/documentation/tutorials/templating-with-k2-and-the-concepts-of-sub-templates)

There are no plans to add a description for tags (but I'm sure there's a plugin for that). In K2, we must say no to some features. If we add everything imaginable as an option, K2 will just become an options monster. The fact that Joomla does it, doesn't mean it's right. If things were right in core content management in Joomla, we wouldn't have made K2 in the first place... ;)

You're welcome.