Based on your 3D object is a file or raw data, if it's a file, the pressure will be on the storage, you can use CDN to serve those files, here I will suggest you to use Next.js for both frontend SSR and serving API, and it will be more easy to maintain since there is only one instance.

If 3D object is storing as raw data in database, the pressure will be on the backend, you can use Redis cache to reduce the expensive requests, here I will suggest to separate the frontend and backend.