Jardinier, what a brilliant project, sadly I don't have a basement so cannot copy it. I especially liked the pipe bringing cold air into the floor area, then venting high up.
sounds like you have got it right,I use to have a pantry with a marble cold slab ,it kept things cool and a good place to store all those jars and bottles.I wish I had one now,you do have to be careful of damp and have it well ventilated.
We have some friends who built something similar in the stone barn attached to their house. We have a cave (cellar in English) but unfortunately my husband uses it for all his tools; I have got my big chest freezer down there, perhaps I can quietly start spreading out a bit!
I have just put some lamb to marinate in my unheated studio overnight, I feel the 'fridge would be too cold and the house would be too hot; a goldilocks situation