Randomness and increment of nonce in GCM
Is it safe to use non-random nonce in GCM? Say I use 0x1 for m1, 0x2 for m2, so on.


It is perfectly safe to use a non-random nonce in GCM, as long as you never reuse a nonce for two different messages.  So, if you use the message count for the nonce, that's fine; if you accidentally forget that you used nonce 0x5 for a message, and use that again, well, that's not so fine.


  How much should a nonce increased for a file?


The file size doesn't matter; use any increment you want (other than 0).  You don't have to increment the nonce more for large files.