Hello,
Did you look at CBJuice? You can find it here:
extensions.joomla.org/component/option,com_mtree/task,viewlink/link_id,2613/Itemid,35/
It lets you add/modify users via a CSV file, and according to "com_juice.txt" in the zip file:
"A password generator has now been added for add mode."
(although I haven't tried that yet)
This should help you for the mass creation of users with temporary passwords. As for the rest (prompting them to change their password and update their profile), I have no idea
Denis
(I'm new to CB, hopefully I did not say anything stupid