Career Advice About Sinch

I'm defining a career path for my company, and don't know where to start. I would like to see how Meta, Google are doing this so that I can tailor to match my smaller company.

Say i want to automate an e2e test for a complex user journey of my web application, i assume that test should automate on a running system and interact with the system like real user (so, no mocking whatever).

How do we create and manage test data? Should automate the creation of test data as well? or ? Please advise.

Can you give an example for this case: a user buying a product, goes through the checkout process with real payment using Paypal?

What kind of tools that Facebook uses for A/B testing?

Are they doing trunk-based development?