Have you ever set up a Software Testing function/team from scratch - what’s the most critical first step?
Bonus bytes for sharing your top software testing thoughts 
I’m not that familiar with the phrase ‘set up the function’ so had to look it up. By definition, I got:
“set up a function” in occupational terms means creating or establishing a new operational unit, team, or department to fulfill a specific task or goal within an organization.
I wonder how can one create this role from within an organization when they are already in a testing role. Or does it mostly refer to those in non-testing roles creating this role?
I’ve been twice in roles where I could have built a function.
For one, I was initially a consultant and then interviewed internally for a manager position. The hardest thing was getting a budget for a team, which was never approved. I ended up being just a solo tester in a product development team.
The second time, the hardest thing was about the business revenue increase and costs. It ended up with restructuring any testing position and the testing being done by PM/BA.
No success story on my side, but curious how others have done it…
Other: Working out what the organisation needs.
Those options jump a lot to the HOW but first we need to understand the WHAT and WHY!
Unless you work in a very very stable organisation things will change. Managers will move, new will come with totally new ideas about eg automations, customers will change. Focus on the people from the beginning. Make management come up with money for team building, go somewhere outside office, get to know each other. For sure, have seminars about strategies and tools, but focus on you as people and team.