Hello,
(1) Yes, multiple instances of Orthanc can run on a single server.
In such situations, I would highly recommend you to favor a Linux server. Indeed, creating a Windows service (as the one that is shipped by the Orthanc project) is a complex task. Read for instance the following link:
But, the official "Orthanc-1.0.0-Release.exe" binary does not implement the "ServiceMain" callback function by itself:
As a consequence, this binary cannot be run as such as a service. You will have to create a C or C# wrapper service above the Orthanc command-line server. There are many tutorials around, e.g. on CodeProject:
(2) The official Windows service of Orthanc will put its logs inside a "Logs" directory next to the data folder.
(3) The parameters of the Windows service are stored in the registry, inside the key "HKEY_LOCAL_MACHINE\SOFTWARE\Orthanc\Orthanc Server".
HTH,
Sébastien-