The full list of Forza 6 achievements was posted yesterday: http://www.forzamotorsport.net/en-us/news/fm6_achievements
Some of these look easy, some of them, well… not so easy. Also, the achievements reveal that there will be "mods". Apparently these were launched at E3, but I haven't yet read more information about them, they say they'll describe them more in a future post.