Ask HN: What's on your SaaS launch checklist?

I'm preparing to launch my company's first B2B SaaS product (a specialized tool for spatial ecologists) and want to make sure I'm not missing anything important.

What items were on your launch checklist that proved essential? What do you wish you had prepared before going live? Looking for both obvious and non-obvious things. Particularly interested in:

- User onboarding that actually converts - Account/user management must-haves - Subscription systems that don't cause headaches - Support infrastructure that scales - First-week metrics worth tracking - Any legal/compliance gotchas? - Did you do a soft launch first? How did that go?

Any hard-learned lessons from your launches would be extremely helpful!