How do you keep up with users/customers?

I have a small B2C website with ~10k users. Currently I send a "Set Your Password" welcome email using Mailgun from Django. But I'd like to proactively reach out more so I can really get a sense for how I can best help them with every change I make.

The touch points I'm currently interested in are:

• Conversation starter "hello" email when they sign up. (I set this up manually currently.)
• For highly engaged/retained users, I want to send a calendar invite to talk more.
• For people who sign up/log in once but then bounce I'd like to send a one click email survey asking why the "sales/marketing" failed for them.
• For people who use the product for a while but then churn, I'd like to send some open ended exit questions.

Who's doing these sort of these things? Am I missing anything you'd recommend? What stack are you using to get this done?