SMOK sp. z o. o.

Best advice will be to put a reverse proxy nginx routing certain calls to frontend, and certain to backend. Best way to build will be Docker images and a docker-compose file for starters, where you will define the database, the backend, the frontend, and the reverse proxy nginx, which you can configure to use certificates and certbot from Let's Encrypt. You can worry about performance later, at which point you will probably need to migrate towards Kubernetes. Standard setup with docker-compose should serve you well for up to 1000 users. You can initially use the same domain with possibly /v1 routing keys towards backend, and the rest towards frontend, which should be a plain Nginx image with all of the frontend files compiled. You can compile them using multi-stage Docker builds, or just plain CI/CD such as GitLab.

We chose Python as our core backend language.

Python enables us to deliver new features quickly, and with the added type annotations in Python 3 typing is not an issue anymore, thanks to using smart IDEs.

Furthermore, it's concise and teammates have no problems understanding or writing it.

We used PHP for a quick hack, which is the contact box on our website. It has a strong point of not needing much, and being available pretty much anywhere, cheap.