For bathrooms, ASHRAE 62.99 recommends that you exhaust 25 cubic feet per minute (cfm) with a continuously operating fan, or 50 cfm with a fan that you turn on and off as needed. Note that you might incorporate a bath fan into your overall ventilation strategy.
Buy a pane of glass that is 1/16 in (1.55mm) smaller that the window opening on all sides. Chip out any old putty. Clean out the recess, and paint it with primer. Lay a bed of fresh putty in the rabbet in the window frame. Press the new piece of glass into position around the edges – not in the center, where it could break. Insert glazing brads or clips to keep the pane of glass in place.