Hi Timo,
1. Is the Wily Introscope Enterprise Manager installed together with the SAP Solution Manager, as I haven't found any download file for Wily Introscope?
No, You need to install Install Wily.
2. What's the standard path to Wily Introscope Enterprise Manager?
Read - 797147 - Introscope Installation for SAP Customers
You would be getting a RTV version for WILY as a complementary version.
3. Where to find the SAR Archive, Management Module SAR, eula and osgi?
Everything is there on market place and then when you uncar and install, you get the rest on the system itself.
For more, refer above KBA - 797147 and guides.
https://websmp205.sap-ag.de/~sapidb/012002523100019353352014E/SAPISDOC95.pdf
Best Regards,
Divyanshu