Thanks for the update.
One question I do have is that I was wondering if it/s possible to train the model server side only, ie not issuing a request through the Slicer GUI?
Yes, you can run MONAI Label without starting the server. Here I explained how this can be done for batch inference: Can TotalSegmentator segment maxillofacial CT as well? - #9 by diazandr3s
But you can do the same for any task. For training, just change this argument to train: https://github.com/Project-MONAI/MONAILabel/blob/main/sample-apps/radiology/main.py#L297
It just works as a standard Python script.
Hope this helps,