Maybe some platforms sticking out for AA guns. Cruiser sized guns never worked on carriers. I would reccomend dual purpose guns.
Depends on the timeframe. Pre-war carriers did in fact have them.
The guns and magazines would take up valuable space and weight. A carrier would also suffer from very thin armor. Having armored flight deck was limiting carrying capacity enough, but adding armor to withstand 8 inch shells would be catastrophic for the air group.
Doesn't change the fact that it was done.