We do a lot of Multi Engine as the first commercial, then single engine add-on, then ME as the first CFI then single engine add-on. That way we avoid having to keep a single engine retract on the line. Most clients want the additional ME time also. For ME as your first commercial, you have to meet the ME experience requirements: 20 hours, day and night dual XC, long Solo(with instructor) XC, 5 hours night, 5 hours Instruments, all in a cheap twin.