This is not a simple or easy question to answer. There are whole courses dedicated to software project management.
Some basic questions to ask yourself:
Testing
- This depends on your project management approach and testing duration. What is the degree of risk tolerance in deploying something with a bug?
Transition to production
- Do you have a cutover strategy? This can be simple or complex.
- Do you have an install plan? What are you assumptions and what will you do if something goes wrong? Will this be heavily automated, e.g., Laravel Forge, or manual? If manual what are all of the DevOps tasks? Do you have a checklist?
- Have you drafted the workflows for support maintenace? What are the channels of communication; how are issues tracked & managed; how will issues be tested, resolved, and fixes deployed?
- What is you plan for preparing the server, installing code, preparing the database, smoke testing, and turning the system on?
- How will you sign-off on the deployment?
Maintenance
- How will you (aka the support team) monitor and track errors that users report?
- How will you monitor errors that the users don't report, e.g., will you monitor the error logs?
- How will you analyze problems and document resolutions?
- How will you handle reporting of errors w/ the team & w/ management?
- Are there SLA (service level agreements) you need to abide by?
Edit: What I recommend if you've never done this before is to dry-run during each testing stage. Make a copy of production, deploy as a controlled QA. Then go through the setup steps. Anything that goes wrong during the install, document it and how to fixed it. Rinse-repeat.
Then test.