I'm a little concerned about what happens gameplay wise after you beat Ganon. Is it free play to do side quests and collection quests or is it like OoT where it just loops back to before you fought Ganon?
A bit of both. You get a star next to your save file to show you've defeated Ganon, and anything you've done since the last save such as photos for the compendium or Koroks found are saved into the 'starred' file. You can then carry on and do whatever you want - but it will still be 'before' Ganon in that the castle will still be possessed and Ganon undefeated.