Your on the right track. I went from Private Pilot and then did the multi-engine add-on. Then I did some instrument training in a single to get the basics down then finished up and flew the checkride in a twin to build some more multi PIC time. Then I started the commercial stuff from the right seats of the single and the multi since I knew I'd be getting the instructor tickets soon after. On checkride day, I flew 4/5ths of my single engine commercial checkride in a fixed gear 172, and swapped planes and did the complex airplane operations in a twin. After the touch and go landing demonstrating the complex airplane operations, we flew out of the pattern and I did the multi-engine manuevers. Didn't have to do an approach since I already did that during my instrument check-ride in the multi. Got back and signed the commercial single engine ticket, handed it back to the examiner for the commercial single/multi ticket. I only paid for one checkride but I made up for that savings with the multi add-on to my private. But, I had logged 25hrs of multi time towards my 250 required and had my PIC time to instruct when I did my MEI. Do the math and I paid half price for my multi time!!! Only thing that sucked was I had to get 10 hours in the schools complex single before I could teach in the f*cking thing because of the wording of their insurance policy requiring experience in a SINGLE engine complex airplane!!!