According to the agreement, I have to pay a fee of €5,00 to SPACEGOATS for each implemented product if I decide to not sign the contract. Do I have to pay for each ASIN or each article?

No. You do not pay for each product. The fee has to be paid for each ASIN implemented by us and only if we have already implemented your product into the Amazon Seller Central before you decided not to sign the contract in the end.