First question: It's possible, but I doubt Qualtrics has a built-in callback to send an email on account creation. Easiest way would be create a test account to see if any email is sent. APIs are usually silent actions that you have to use other APIs to follow up on. In their API documentation for a survey's response exports, it takes three calls. 1) Create the response export file, 2) get the status of the export file (percentage), and 3) return said file.
Second question: Even if you can get an email, there's no GUI to support modifying the email, unfortunately.
Third question: This I believe is entirely possible. I'm thinking maybe a webhook listening for account creation would be the way to go on this, you'd just be responsible for building the vehicle to receive the webhook (Teams channel potentially?)