To use the RPi via Remote Desktop, different protocols and programs exist, i.e. VNC. Due to simplicity of use, however, I mostly chose XRDP, which works with the Microsoft Remote Desktop Tools. However, you must not install it via sudo apt-get install xrdp - as this will install it with realvnc and break xrdp (Package error which has not been fixed yet in the recent "Pixel" Release of Raspbian...).
Instead, use:
sudo apt-get install tightvncserver xrdp
As it will install tightvnc first and xrdp will use it after that as source. You can then use mstsc on your Windows Machine or any other RDP Viewer to access your RPis Desktop.
PS: Yes, the new Pixel Version of Raspbian does contain an VNC Server which can be enabled very easily via the GUI "Raspberry Pi Configuration" Tool, if you want to use VNC directly without RDP. However, I did chose this way, as the old VNC server installations never worked for me and I got used to this kind of "workaround" (more or less a "works-for-me"(tm) solution)
Finally something that works. Thank you very much!