According to my understanding, you do not have to care about the questions like Wx + b or xW + b in Pytorch.
When you have 100 * 10 input, it means you have the input data with batch size 100 and dimmension number 10. After the processing, the output of the neural network will be batch_size * output_dim, which is 100 * 1. So your current way of writing this is right.