Recommendations of boards

Projects General Guidance
7

  1. I have not used the Arduino Micro but it appears from the photos to have a white dot near one pin of the ICSP which designates pin #1. The USB host shield should have a similar white dot. Line up pin #1 to pin #1 and it should work. There are other pins that must be hooked up as well so check the USB host shield docs.

  2. I have not used the load sensor or the RFID reader/writer so I have no idea about the final code/RAM size.

I can only suggest compiling sample programs for the load sensor, RFID read/writer, USB host keyboard, etc. and see how much Flash and RAM each one takes. The sum should give you some idea of how Flash and RAM will be required for the final product.