Salesforce DevOps Automation for managed package generation with JIRA/BitBucket

We want to automate part of our internal QA process that requires the creation of a new managed package, creation of a new sandbox, and installing the new package in the new org. Additionally, we’d like to create a few new users in the new sandbox for specific people.

Environment and Platform:
We’re using JIRA and Bitbucket and we’d like to use Bitbucket Pipeline (unless there’s a good motive to move outside the Atlassian environment).

Trigger:
When a Pull Request is created in Bitbucket.

Automation steps:
Steps
1) Code Deployment to test org
2) Creation of managed package
3) Creation of a new Sandbox
4) Create users in the new Sandbox (#3)
- the users may change overtime so this can't be super hard to change, we're ok with hardcoded info as long as it's changeable
5) Install the package (#2) in the new Sandbox (#3)
6) Run post-install scripts in Sandbox (#3)
- This is just running a 1-line apex anonymous line.
7) Assign permission sets to new users (#4)

Notes:
- Steps 2 and 3 should be started in parallel.
- We want some Error reporting