I cannot answer all of your questions, but I can say that if you are trying for realistic renders, under Render Settings you select the Nvidia GeForce option. CPU should almost never be selected.

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System: Lenovo Legion Pro 7 16IRX9H Laptop | Windows 11 Professional | 32GB RAM |  14th Gen Intel® Core™ i9-14900HX | Nvidia RTX 4090 Laptop GPU 16GB 9728 CUDA Cores
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