@Ward Horsfall Thank you for reaching out to us. As I understand you are looking for inputs related to RAM for Azure AD Connect/SQL Server Memory.
To begin with, you can refer to below table for CPU/Memory/Hard Drive minimum requirements for the Azure AD Connect sync server
SQL database factors:
The size of your source Active Directory topology will influence your SQL database performance. Follow the hardware requirements for the SQL server database and consider the following recommendations:
Organizations with more than 100,000 users can reduce network latencies by colocating SQL database and the provisioning engine on the same server.
Due to the high disk input and output (I/O) requirements of the sync process, use Solid State Drives (SSD) for the SQL database of the provisioning engine for optimal results, if not possible, consider RAID 0 or RAID 1 configurations.
Don’t do a full sync preemptively; it causes unnecessary churn and slower response times.
Reference:
https://learn.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-install-prerequisites#:~:text=Hardware%20requirements%20for%20Azure%20AD%20Connect
https://learn.microsoft.com/en-us/azure/active-directory/hybrid/plan-connect-performance-factors
Let me know if you have further questions, please feel free to post back.