Hi Stefano,
Thanks for the prompt response. I can see from the link you sent that Newsletter does/can rely on the native WordPress Cron.
The only outstanding question I wanted to confirm was this one:
2) As an extension of #1, is WordPress site activity from visitors directly related, or related at all, to how fast Newsletter sends its emails? In other words, will Newsletter continue to send emails if there is no activity on the site? Additionally, if there is an increase in site activity, will the rate at which Newsletter send its emails also increase?
Thanks,
Matthew