For enabling SSL you can take a look at the relevant guide here. You’ll want to be aware though that users will have to recover their accounts once you enable this!
As for Duo as your MFA option we have this guide. You’ll need to do the SSL configuration first though.
For enabling there are 2 places to do this, the first being under the Administration tab. This will enable it for your organization. Then each user will need to go to their profile and enable it there as well.
Yes there is an option for that. When you copy or create the first thing each time you log in you’ll be prompted for your password again, but then you can use the drop down to select a longer time to not have to re-enter it right away as seen in the attached image