Please spend first 90 days building a good reputation and impression for yourself with your supervisor and coworkers and later use your reputation to drive any changes. By insisting on using Arch Linux, you will be wasting yours and others time in accommodating your preferences in recreating the workflow and tools that everyone else is used too.
You should focus on learning the tools and workflow used by your employer. You are no longer a freelancer who can chose their own tools and workflow, you are a cog in a machine now and learn how machine operates.
Your first priority should be to learn Windows and Development tools used by your coworkers. Find out what PHP framework and technology stack being used. And learning them is your next priority.