For me, it depends on where I am going exactly. For example, I rarely bring more than a single pair of shoes, unless I’m expecting to go somewhere formal or sandy. One set of clothes per day is usually enough, unless I’m expecting adverse conditions or laundry access. As far as space vs weight, space is fixed by the bag whereas weight is limited by what I can carry and for how long.

Just running through the days and any plans you know of should help, taking the expected climate into consideration for quantity of spares.