The GraphQL that powers flyctl can do everything you need, but we don’t have a Terraform provider.
We’ve looked pretty closely at Pulumi, it shouldn’t be too hard to build a Pulumi provider for Fly. We just haven’t done it yet!
You might be able to do what you need with flyctl and some bash scripts, however. fly regions set, fly scale count, are fly scale vm are idempotent, you can safely run them over and over. If you create a bash file for a given app config, you can just run it over and over. You’d still have to create the initial postgres clusters and apps first, so it’s not perfect. But this is how I’d start.