In this context, Gargamel is being very optimist and is making the claim that his fortune is already realized and that he will have a prosperous life thanks to the tree trunk made of gold.
You are right. “Faite” is an adjective and it means that Gargamel is rich now.
Vous avez raison. “Faite” est un adjectif et cela signifie que Gargamel est maintenant riche.