Definatly do both from the start.
Like bb77 said, your body needs energy to work the muscle's and the more muscle's you have, the more energy you need, the quicker you will lose weight
And Rayray has a very good point about the saggy skin and muscle tone
I think if you do cardio one day and toning the next, you should see some pretty good results. Try not to walk to quickly. Even pace, so that you can keep up a conversation.
You can always try walking with wrist/ankle weights, just to help the toning along, or even try jogging for a minute and then walking for five and then jogging again, to burn more fat.