As the holder of an ICAO ATP you can skip the FAA commercial if you want. 61.153(d)(3) allows you to go straight to the ATP level. Or you could get a commercial SEL and then do a MEL ATP if all you want is a commercial SEL. The commercial checkride is mainly a bunch of visual maneuvers while the ATP ride is a fancy instrument checkride. Any way you do it should only take two checkrides.