I have two questions - which are not explicitly addressed in the Atlassian documentation on the web.
Is the ability to add external users (guest) available in the "Standard" plan? Or is it only for Premium and Enterprise plans.
It is stated that the guests are free of charge (up to 5 guests per paid user). Total number of users (paid + guests) can't exceed the current Confluence site. So, one needs to be withing the user limit of 50,000 for standard plan - and there is no such limit for other plans.