1) I don't use a local instance so I might be wrong here, but maybe you have a type in the port - PostgreSQL port convention is 5432, not 54322
2) Never seen this, but I don't see how this can be a Supabase issue and NOT a PostgreSQL issue (which would be a very serious bug, so it seems more likely that the issue is with your SQL definitions)
3) You can connect to the online instance directly via any SQL console/workbench (e.g. psql, TablePlus, Supabase dashboard, etc) and execute the seeding statements from there. DB migration tools such as FlyWay also allow you to define migrations that seed the db and they also connect directly to the db (i.e. they bypass the REST APIs)