SlicerVMTK extension is available in Slicer-4.11. There are some temporary issues with the extension server today, but you can use a Slicer release from a couple of days before, for the version that you can download from here: Download 3D Slicer | 3D Slicer
@jcfr @Sam_Horvath many extensions reported upload errors - see for example this.
If you installed SlicerVMTK and the modules did not appear then maybe you have closed the application manually before the installation has been completed. The installation is completed when “Restart” button becomes active.
“Centerline Computation” module performs network extraction. You can process the network further and extract additional data by Python code snippets as shown here.
If you can describe the clinical problem you are trying to solve and the analysis that you would like to perform then we can give more specific help with how to achieve that.