I intend to do the Commercial Multi Engine as my initial, and then followed by the Commercial Single Engine Add-On
Here's how I did it, but at that point I only had a PPL IR ASEL, I decided to get both the CPL ASEL & AMEL and on the same day. Meaning I first went out in the good old C152, did all of the VFR stuff (commercial maneuvers, like lazy eights, chandelles etc.). Then I went out with the multi and I did the instrument and the single-engine stuff. I basically did the "multi" as an add-on and so I complied with the "complex aircraft for CPL checkride" and I saved myself from the hassle of scheduling another check-ride, since it was all done on the same day, saves time and money. And in the end I got a certificate saying "commercial pilot ASEL & AMEL instrument rated.