Hi, I used to teach reception until very recently, and I also had a nervous starter myself (my dd).
I agree it's too soon to go into detail about school. The odd mention in passing, so it's on his radar, is a good idea, however.
Over the summer talk a bit more about it, walk past the school occasionally and mention it casually, and go to any transition meetings. When you come to leave him, say goodbye, emphasise you will be back later, and go! Honestly, the staff will not leave him crying alone. We've all spent time holding crying little ones, and in every case but one that I remember, they swiftly stopped crying with a bit of comfort and distraction. We coped with the one that didn't stop crying and he settled too, though it took longer.
My dd cried every morning for most of a term, but I knew she stopped within a few minutes, and was happy for the rest of the day.
It's fine to ring to check they're ok the first few times. Don't expect an instant reply as someone may have to go to check he's ok, and then ring you back!
I think being matter of fact and practical to the child helps - they need to go, you will be back later, that sort of thing. So not unsympathetic to the child, but not making school optional! It will be fine, honestly.