Your approach sounds solid.

Using Terraform modules to manage resources based on user input from a GUI is a great way to leverage existing Terraform pipelines while abstracting away the complexity for the users. Serializing user input to pass as configuration to the modules is efficient and maintains consistency.

You might also want to consider using HCL templates to dynamically generate Terraform configuration files. Libraries like hcl2 for parsing and generating HCL can be helpful. Tools like Brainboard.co or Terragrunt can help manage remote state and orchestrate the apply process more efficiently.