I would like to know when when I provide an .etlt file and tlt-model-key=nvidia_tlt do I need to configure any other things.
yes, other options are also needed, please refer to the tlt config files under /opt/nvidia/deepstream/deepstream/samples/configs/tlt_pretrained_models .
Magic tag does not match
Should indicate, the etlt file or tlt-model-key is not correct. tlt-model-key is the key you are using to generated the etlt file.