Breakfast varies whether they will sign or not. Sometimes it is photos only.
When they are walking thru the ship, it is really up to the character/handler whether they will sign or not. On deck 9 they usually will. On deck 4 it depends on whether they are just "roaming around" (in which case they will) or if they are on the way to a scheduled appearance (in which case, usually not). You will see them ALL over the ship...deck 5, the fitness center, deck 9 as well as all the scheduled appearances. There are lines of various length, but the character interaction is way better than at WDW in general!