For general gstreamer, there is no special metrics. If you want some, trace may be used although it will impact performance .Tracing (gstreamer.freedesktop.org). For Nvidia plugins, the latency of deepstream plugins can be measured but it also needs to be added by code. DeepStream SDK FAQ - Intelligent Video Analytics / DeepStream SDK - NVIDIA Developer Forums
No.
No. No tool to do this
You can run “nvidia-smi dmon” to monitor the GPU loading and RAM usage in runtime.