Older versions of add-ons are available on https://marketplace.atlassian.com
JIRA Agile in particular can be found here.
Download the most recent available version for your version of JIRA and use the Installing by file upload method to get it up and running on your instance.
This should cover all 3 of your questions
This community is celebrating its one-year anniversary and Atlassian co-founder Mike Cannon-Brookes has all the feels.Read more
Hey Atlassian Community! Today we are launching a bunch of customer stories about the amazing work teams, like Dropbox and Twilio, are doing with Jira. You can check out the stories here. The thi...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs