You will need three layers of metal for each repair section, one for the rear panel lip, one for the floor lip and one for the valance lip. That is to do the job properly.
Due to excessive rust i had to replace the full bottom section of the rear panel including hinge area. The full boot lip edge and a complete rear valance.
On my sons car i had to do pretty much the same apart from a full boot floor replacement. I have this job to do on my Clubman as well but the rear panel will be replaced from just under the rear windscreen down and the complete boot floor and valance due to accident damage.
If the rear valance is salvageable then happy days, however from experience the rust travels under the flanges.