In every educational setting I would hope that along with critique of a child's behavior there would be goal setting and problem solving. Unfortunately this is not always the case. In Montessori education children are shown how to respect eachother's space and also respect individual work space. Supporting a child's concentration without interruption is the focal point of Maria Montessori's work.
Some children grow out of taking naps.
A preschool should have the flexibility to meet the needs of your son. If not, it's not the right school for him. I encourage you to observe as many Montessori programs as you can and speak to the teachers. An experienced, certified Montessori teacher will know how to set up the proper environment for your little one to thrive. Please keep us posted and best of luck.