Im guessing a 235/45/17 would be the safest tire size.
Several guys here in my Mustang club mentioned that the 2005+ mustangs tend to float at speeds higher than 100mph if they do not have a rear spoiler. My V6 has no spoiler however i did get one from A.M. Its just a matter of getting it installed.
Welcome to the club CaptainRon! I just purchased a 2012 base also and very happy with it! Yes, sure there are mods that I'm doing to it but everyone has their own direction, thats the fun thing about these stangs. Sure, there are a gazillion on the road but for the most part they all have a personality thats what sets them apart. Have fun with the pony driving and modding most of all make it yours!