Take 3: it finally works... Alright with an added module which automatically launches the minecart if it arrives and the chest is empty. Actually this design sucks but it's functional enough for what I need
Success!
Worked on it more, and a random bug broke the entire working machine. It needs to be fixed
No joy quite like saying "I should make a super smelter!", starting to work on it, getting lost on the redstone, going into a test world, testing ideas, getting lost on ideas, looking up tutorials, tutorials are way too complicated or way too simple, and giving up on the idea