Since we are only allowed to answer one question at a time, I edited your multiple questions and will answer the main one: Is Cherry Orchard considered a naturalist piece of literature?
The answer is yes. The Cherry Orchard represents naturalism in that it presents the reality and inevitability of what life can bring onto someone who has not made right choices, and will present to you with no aesthetic or stylistic devices the cause and effects of things. Naturalism also indicates the presentation of characters who suffer from personal deficiencies and problems that lead them to their fates. You see that even Firs, the poor manservant, was so behind his times that he was literally left behind when the family moved.
However, it is in the sadness that comes with the cutting down of the cherry orchard that the naturalist aspect of the story comes. All is measured, decided, planned-ahead, and will be carried on. No matter how much love or decadence the orchard represents, its symbolism and beauty will not dictate its salvation like it would in a neoclassical or pre-raphaelite work. If it has to go down, it will go down and no matter who cries, despairs, or suffers as a result, life is life, and all is fair.