I found that walking does help, but a lot of guys have expressed the opinion that, as in so many things, moderation is important. Overdoing it can leave muscles tired and perhaps increase leakage. That applies both to the walking and to the kegels.
I don't know what your fitness level was prior to surgery, so maybe four miles a day is no big deal for you. I would just advise that you "listen to your body" and adjust your activity level accordingly.
Overall, though, I would say that you're doing really, really well. Regaining continence is such a satisfying experience, and I hope that happens for you very soon. Congratulations on a great start to the recovery process.