Jigar Dave

My advice will be Front end: React Backend: Language: Java, Kotlin. Database: SQL: Postgres, MySQL, Aurora NOSQL: Mongo db. Caching: Redis. Public : Spring Webflux for async public facing operation. Admin api: Spring boot, Hibrernate, Rest API. Build Container image. Kuberenetes: AWS EKS, AWS ECS, Google GKE. Use Jenkins for CI/CD pipeline. Buddy works is good for AWS. Static content: Host on AWS S3 bucket, Use Cloudfront or Cloudflare as CDN.

Serverless Solution: Api gateway Lambda, Serveless Aurora (SQL). AWS S3 bucket.

If You are targeting monthly active user on more than 1000 then I would recommended AWS Conginto. It is cheap compare to Auth0. It gives better integration with other AWS service. Amplify is good for initial development. I would to suggest separate backend and frontend repo separately. Use terraform for AWS service.