Hello @Nikos.Kyrm 
To backup exchange online you are going to need the following: 

Media agent to write the data and host a DDB

Access node to collect the data from O365
Index server to manage the index data to enable browse/restore

Commserv to manage all of the bits. 

The hardware requirements for these are as follows: 
https://documentation.commvault.com/2023e/expert/hardware_specifications_for_mediaagents.html

https://documentation.commvault.com/v11/essential/hardware_guidelines_for_exchange_online_index_server.html

https://documentation.commvault.com/v11/essential/guidelines_for_exchange_online_access_nodes.html

https://documentation.commvault.com/2023e/expert/hardware_specifications_for_commserve_server.html

if you meet all these hardware requirement's on one server there is no reason it cannot do the work. 

I would just make sure your disks are fast enough as the CSDB/DDB and Index can be quite IO intensive. 

Not recommended but no pain to try. 

Kind regards

Albert Williams

Hello @Albert Williams 

Thanks for your reply, but I don't thing that for only 700 mailboxes it's worth the Azure cost to deploy all these roles / nodes to separate Azure VMs. That’s why Im looking for recommendations for an All-In-One approace.

Also, the sizing from documentation is not clear. For example for Commserve Server, Small size says that “supports up to 25 servers, or 100 virtual machines, or 200 laptops in a single CommCell”

Also includes all the following packages:

I cant find clear hardware requirements only for the CommServe VM. Just for CS role.
 

Best regards,
Nikos

All of those packages are needed to run the O365 agent and all its features. You need webserver, Console, Workflow engine, cloud apps to be able to perform a browse on the data. 
All the other packages are not required but also do nothing unless engaged. 

If you are wanting exact numbers try this (In my opinion may work ): 

Server with 16cores - 36GB of memory - 2 separate 1TB SSD. One for the CSDB and the other for the DDB and Index Cache. 

Give this a crack, if it doesn’t work or is slow increase the CPU. Make sure you don’t cheap out on the disk performance is all i can recommend. 

What you are attempting to do is not recommended as it is not scalable solution so there is not going to be any documentation on it. Just give it a crack haha. 

Kind regards

Albert Williams

Also latest Public-Cloud-Architecture-Guide-Microsoft-Azure CPR 2023E may help, but not mention anything about o365 backup.

Best regards,
Nikos