full-screen background image

I think you need to post up some code - I'm really not understanding what you're after.

drawImages can happily rotate the clock hands and overlay them on an unrotated clock background while updating only the area you specify, so I'm not entirely sure why you'd need 60 different background images.

Honestly, the answer to all those questions is 'it depends'. The best thing to do is to benchmark.

Flash memory is laid out intentionally such that everything is contiguous, so yes, you can just randomly access pixels if needed.