1. Pairing was of coarse Tony/Steve
2. Tony does something with extremis to merge with the suit
3. Tony pretty much fabricates himself to the point where the only way to kill him is to remove the arc reactor.
4. By the end of the fic Tony is pretty much immortal. Its very Ghost in the Shell.
5. At one point Tony get "hacked?"
Hopefully that helps and no it isn't Rebirth. I'm also pretty certain its somewhere on AO3