Wow, very nice and useful cellar. Three doors system should be enought to keep "fridge" temperature inside main chamber. Anyway that will be perfect to storage not only potatoes. If you have so much wood maybe craft some shelves or crates and your cellar will become perfect place to storage jars with fruits, wegetables and mushrooms also always put a pack of beer inside so you'll have acces to cold beer any time - this is my lifehack, recommended :)