Where can I find the "project_id" ?

Otherwise, should this be API related the supported APIS are explained here: https://jazz.net/wiki/bin/view/Deployment/CLMProductAPILanding 

Having said this, DNG has several APIs See https://jazz.net/wiki/bin/view/Deployment/CLMProductAPILanding  and see the APIs supported by DNG. There are two REST APIs, the OSLC API and the Reportable REST API. The OSLC API is the only API of the two that allows updates. There are other server (REST) APIs for special purposes e.g. the module API.

The APIs have a documentation link and there is the OSLC workshop which is outdated, but still provides useful hints. OSLC uses a discovery mechanism to find the service providers (project areas). You get a list of those and each element can be GET to provide details such as Project Area name and Unique ID etc.  I have tried to explain some of the principles of the EWM OSLC API in this series of posts: https://rsjazz.wordpress.com/2021/09/29/using-the-ewm-rest-and-oslc-apis/

EWM is not DOORS Next, however there are a lot of common principles in the OSLC API, especially discovery. So looking at this might be useful. A colleague of mine has used the OSLC API together with Flask. Some more links:

https://archive.open-services.net/wiki/requirements-management/OSLC-Requirements-Management-Specification-version-2.0/index.html

https://docs.oasis-open-projects.org/oslc-op/rm/v2.1/requirements-management-spec.html - Current spec

Use https://www.google.com/search?q=OSLC+RM for more links. I found that interesting as well:

https://softacus.com/work/tag/oslc%20api

https://michaelrowe01.com/index.php/day-job/ibm-elm/beginning-api-discovery-or-understanding-the-rootservices-document/

https://github.com/IBM/ELM-Python-Client is a resource to look into as well.

I'm not aware that there is the concept of the 'id' (an integer?) of a DOORS Next project in the public APIs. You can discover project area-related URLs and other information such as components and configurations (again, URLs) using the supported APIs - there's a walkthrough starting at /rm/rootservices here https://jazz.net/forum/questions/266334/dng-oslcfetch-components-from-project-area/266667

It's important to use discovery and NOT EVER construct or hardcode URLs because hardcoding is very fragile across versions.

As to the practicality of your approach, all that's needed to access the REST/http APIs is a programming language that can talk http, and Python is certainly capable of that. AFAIK there's no need to run a http server such as Flask to use the APIs as a client.

HTH

Ian