Please keep in mind that you cannot mix different licenses in Enterprise Manager, so you should be running Enterprise Plus for all servers and upgrade your 2nd and 3rd backup server to 9.5.
Enterprise Manager doesn't require a specific location, it depends only on your preference.
If I get you right, for the Monitoring team accounts you can give role named "Portal User" and edit permissions to restrict unnecessary restores.
The recommended way for monitoring purposes is to use Veeam ONE
. This will provide read-only access to the entire backup infrastructure for your team.