You don't NEED a lisence - if you're doing it home based. You're really not "starting a business". You're just doing this to get some extra money, by doing something you don't mind doing.

I suggest you get some good quality shampoo if you plan on doing this. I reccomend picking some oatmeal shampoo up from your local vet (about $14 a bottle - but smells very good and is very mild on your dogs skin ).