I think the long summer holidays helps them forget pre-school, in a good way iyswim, as it is then not such a drastic immediate change. Also not going on to much about NEW & BIG school, try not to make it sound daunting and scary. You are lucky that you have two good schools that he may go to, just see what the decision is and take it from there. Don't talk to him about first and second choice schools, it will make no sense to him at all, more confusing. Also remember that if you don't get what you want, don't panic, people drop out for many reasons, moving, going private, wanting second choice, so if your first choice is full up, it might not be the case after a couple of weeks. When you do know a final choice, walk past the school a few times over the summer hols, make him familiar with it, try on the uniform.
DS2 started in reception in September, he was with some friends and there were some totally new children, and honestly after a few weeks they were all fine and settled. This one little girl sobbed everyday for a week, he poor parents were beside themselves, but she the just loved school and now bounces in every day.
Most stagger the start for reception children eg: a week of mornings then a week of afternoons, something like that, so they get used to it in smaller doses.
I think the calendar thins is a bad idea, makes too much of a big deal of it all, countdown too much! Just enjoy the Summer, talk about school, how much you and Daddy liked it, what fun things they will do etc etc.
They are so cool about it, while the parents are in bits. I had to sob in Costa on his third day, he was my last child to start school (Have older DS1) and it was a momentous thing for me. He loves school and has already packed his book bag for when he starts back on Monday after the Easter hols!