The current implementation of RadAsyncUpload does not allow storing the temporary files in a memory stream.
As per your second question, can you, please, elaborate a bit on the exact behavior you are facing? A video demonstrating the scenario along with the AsyncUpload setup you have will be very helpful in understanding the scenario better.
By design, the AsyncUpload does not remove the input for the canceled items, you can see a video demonstrating that here:
You can keep the count of the upload inputs the same with a similar setup (the code below will show always 3 inputs):
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