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1. you can use this one . print it out, and laminate it (FLAT !) on some board.
2. size depends on distance. A4 will do for <1m.
3. take like 10-30 images, use oblique angles, and see, that you have the whole field of view (esp. the corners!) covered.
4. no
   

you also want to look at the tutorials, and probably use the calibration app here