Is there any article explaining steps to pull in the AD user data into the user info list?
At the moment the list contains only users who have logged into the SP site. Can I pull in all AD users?
Can you describe WHY you want info in the User Info List? Generally you sync with the User Profile Service and leave the User Info List alone. I think you don't understand the architecture. There are many great guides on the topic, the best by far is Spence Harbar's: http://www.harbar.net/articles/sp2010ups.aspx
It says 2010 but applies to 2013 as well. You can also use direct AD sync in 2013 which may be all you need.
User entry is only added in the User Information List when the user logs into the site. What you can do is to read the user from the AD and then call
SPWeb.EnsureUser. This will add an entry in the User Info List for the user even though user has not actually logged into the site.