The question of whether Peter should be involved with Marauder shenanigans is always a hard one for me! I was never particularly into Marauders-era fic, and I think this is one of the reasons why: he was one of their close friends, so clearly they liked him; but it is hard to reconcile that with the kind of person he is when we see him in the books. So no matter what one does with him in a fic, it feels weird to me.