Power BI Embedded and AAD Edition

My customer wants to use Azure Power BI Embedded to provide reports in their customization portal to external users (such customers or vendors), so they have to buy:

1. Power BI Pro for developer

2. Power BI Embedded

3. Do they have to buy what's kind of Azure AD edition or just use free edition (under 1,000 external users) ? https://azure.microsoft.com/en-us/pricing/details/active-directory/

Thanks in advance!