There are going to be covenant more then likly, also the interutpting Halo 4? They are giving it more story, idk if you have read the books or not but he does get Mark IV around that time (that is for everyone not you in particular). Also the one thing i'm concerned about is if Master Chief has shields, he should not have any shields at that time so that is the thing i'm concerned about.
Oh, to go with the armor thing mark IV resembles mark VI sometimes so....