I walk one dog at a time or up to 4 dogs at a time. I would never walk more than four dogs as I feel that as a dog walker, you need to be aware of what's going on at all times. By walking large groups of dogs, it limits your control over the situation! Plus, by walking only small groups of dogs or walking only your dog, I can provide a more attentive service, meaning they get more interaction with the walker and it's just generally a better experience for them.
Living in North London, I am very fortunate to have lots of parks and green places to walk the dogs. Some of the parks where I walk and your loved ones can have plenty of fun is Alexandra Park, Highgate Wood, Priory Park and Finsbury Park.