Re:where should i fit deadlift in my routine?
It can be done on back day. But it can equally be done on legs day. This represents the fundamental conundrum with body part splits. If you have deadlifts in your routine (which you should), and your routine is a body part split, then the premise of your routine is automatically moot because deadlifts work both your legs and your back and so you are never completely splitting up these muscle groups.
Still works for people of course, much better for those on gear though in my experience, but I just find they make little sense in a lot of ways.