You should be able to just change the rings.

The bolts are not supplied with these chainrings.

Any 110Bcd/Pcd ring will be compatible. 39T FSA would fit.

Yes they are.

Only if Campag chainset also has 110 BCD already.

Truvativ Elita cranks use a 130BCD setup. I will link some options below.

You will need to use a 130 PCD/BCD ring to fit the cranks you have. I would also recommend sticking to the current ratio unless your front derailleur can handle a larger gap then most. You should be sure that your deraillaur can handle a 19t gap between the two rings.

The 7900 chainrings are designed specifically for the 7900 uni-directional chainset. You should not use these unless you have a Dura Ace 7900 chainset already.

This is a 10 speed ring, I would not recommend using it with a 7/8 speed chain. The chain is too wide and I can't guarantee it will work.

Yes this chainring should be fine for use with your Shimano Hollowtech II chainset.