Capture and display users name

Use wp_get_current_user to get the current user (if any) then check or update the display name – update_user_meta or wp_update_user.

When you have a user, you’ll probably want to set a flag on the user’s meta for after they have filled out their name, or prompt otherwise.

How/where all this would go is really a more complex discussion than the root of getting and setting the data. Most likely this should be done via AJAX so the initial page is rendered, and the hello decorates it after the fact.