Fearful/Reactive Behavior

I have stopped taking Kodi to any more classes and limiting his walks where he can have reactive episodes with bikes, scooters, loud cars, people, other dogs (you name it he is reactive to it). I want to take the summer off. When we have visitors, I keep Kodi behind a gate, especially for the first half hour. Initially he will react by barking but eventually he quiets down and accepts the person/visitor. He will lay down very peacefully unless the visitor uses his hands to "talk" or gestures with his hands or makes any sudden moves. Then Kodi starts barking again. Sometimes I have Kodi lay next to me in a sit or down stay and that keeps him pretty calm. I do believe that over the past several months Kodi has calmed down some, but I can't completely trust him. If, heaven forbid, he would bite someone, I would feel terrible. I must be ever vigilant with him while at the same time trying to get him less reactive. I have read many, many books on the subject: Turid Rugaas, Patricia McConnell, Karen London, Karen Pryor, Ali Brown and I can't remember the author who wrote "Control Unleashed", which by the way is a great read with good advice. However, it all takes time.