We’ve gone through a name change at our company recently and we need to look at mass updating everyone’s email. Am I right in thinking if we do this, it’ll force everyone to create a new password, and also remove access?

I just tested this in the UI but it looks like you'll have to edit the employee record, check the box to give a new password and actually give them a temp password and then check the box to require a password on login and save the employee record. Access did not seem to be modified.

I would expect it to wipe out saved preferences and the like. (Shortcuts, Sticky fields, etc)

That won't change anything as far as their log in. It would only affect it at the employee record and mainly visual change. The change should be in Settings > Change Email for each user. Unless you remove access for everyone, change the email and provision again, but that sounds catastrophic.