A dog who is "leash reactive" is most likely experiencing some anxiety, fear or discomfort associated with other dogs. The situation is worse on a lead because your dog can’t approach in a safe and relaxed way.
Many dog owners prefer to leave haircuts to professional groomers. It’s a job that really takes some know-how and experience to do properly – particularly for dogs with long, continuously growing hair. But there's no reason you can't become an expert.