The back door to the Taylor's home opens right into the yard. However, in the episode "Bargain Day", the back door opens to a back porch where the freezer is kept.
At one time, local telephone lines were strung through trees. Don't know if this was still the case by 1960's but considering the use of "candlestick" phone in courthouse it might have been possible in timeless Mayberry.
Thinking Opie has a real horse, Barney suggests they go outside so he can show everybody how "Blackie" would take to him. Yet, in the episode "Divorce, Mountain Style", Barney claims to be allergic to horse hair.
Mr. McBeeVee is a utility lineman and is seen on a utility pole.
There is no reason a lineman would be climbing a tree in the woods where Opie meets him.
When Barney, Andy and Opie go outside to see "Blackie", the shadow of the audio boom and the mic are clearly visible across the back screen door.