You';re right, the automations are handled by the cron job. In case you want to test all you have to do is to create a mass action instead of an automation. Mass actions are executed manually where as automations run automaticly when triggers are activated.
In order to use your automations you would have to activate your cron job. V5 and v6 each have a different cron url. Technicly it's possible to have two cron jobs, one for v5 and one for v6. I just don't know if this is allowed on Acyba's cron server. You can try it, you always can revert back by disabling the cron in v6 and re-activating the one for v5.
You newsletters are never sent via Acyba's servers. It's your Acymailing that sends the newsletters out, it's just Acyba's server that's triggering yout cron job.
Correct, the easiest way to send a newsletter to all subscribers in a list is to create a campaign and send it immediately or schedule it for a given moment in time.