Will I get OTA updates from Vodaphone Australia by flashing stock I9300XXEMC2 ROM on Samsung Galaxy S3?
Will I be able to get OTA updates if I install this?


CSC of XSA or VUA works for Australia. As long as it's stock ROM, you should be able to get OTA update. If it doesn't work, try to update via Kies on your PC.


  I've read that it might have problems if the modem and CSC don't match
  up.


It's OK for modem and CSC to be different, but CSC must be correct if you want OTA updates.