That solved ALL the issues 
So basically everything was correct but for the fact that localhost:5000 had to be replaced with ae_graphql:5000 in the Caddyfile. Similarly localhost:4000 had to be replaced with ae_json:4000.
This makes complete sense in hindsight. Using new technologies for the first time tends to be quite an adventure…
@francislavoie please have a beer and enjoy having saved my ass! I can’t thank you enough.