1997 Mercury Sable Computer codes

first code reading after a miss and rough idle pointed to number 2 spark plug bad. Changed ignition wires and installed new plugs as it was time anyway. Ran a little better but still not right. Read codes again this time codes said number 2 coil pac and number 2 injector problems and main computer problem possible. Before I slap on a new coil pac could a bad injector ruin the coil pac? Should all the coil pacs be replaced if only one needs it? Should all the injectors be replace as a set if only one needs it? This the basic OHV engine NOT the duratec OHC.

Thanks, any help appreciated