Hi nitpas, you can find a specific section for cluster installations under the McAfee ePolicy Orchestrator Installation Guide; you'll also find a sction for upgrading ePO on a cluster installation.
As for the servers themselves you'll need at least 2 servers for ePO clustering and 1 or 2 servers for the SQL server if you want to cluster the database.
Should we first go to the Upgrade to 4.6 version and then make a cluster or do we need to make a cluster first on the existing 4.5 patch 5 and then upgrade. Which one is more fessiable and can be a best practice?
Laszlo has already referred to the ePO installation manual and this manual says you need to have your cluster set up before you'd install ePO in a clustered mode. So you'd need to reinstall ePO anyway if you wanted it to be clustered installation (because you cannot just upgrade and make it a cluster at the same time).
But because your SQL server is at the moment "ePO 4.5 version structure", please
1. back up ePO 4.5 server and SQL server in their current state,
2. upgrade your ePO 4.5 to 4.6 so SQL database containing data also gets upgraded,
3. and if that went okay, back up the SQL server and ePO server again (already in their 4.6 version state),
4. make your (ePO) server cluster, then
5. reinstall the new ePO 4.6 in cluster mode (you might need to deinstall ePO 4.6 because new installation should have clustered resources) and
6. connect it to the already ePO 4.6 structured SQL remote server.
This is how I see your intent to complete from single ePO/remote DB into a cluster ePO/remote (single) DB.
When you want your SQL server to be also in cluster mode, that adds a few more steps in this process between steps 5 and 6 I think.
To answer your original questions:
1. you'll need 2 servers for each cluster (for ePO and for the DB if you want both clustered) and that makes 4 servers.
2. please elaborate this question...
3-4. ePO server is supported on physical and in certain virtual environments as follows: https://kc.mcafee.com/corporate/index?page=content&id=KB51569 . According to the installation manual, there is no specific instruction as to the systems should run on physical or virtual servers, it is your decision.