Ok, as a CFI, here's my interpretation of it all...
If you do it under a 141 program, the long XCs and night solo, etc... must be done while you are training for your commercial. Same goes for the instrument. Under 61, I think it could be done anytime. I could be wrong, so please correct me if I am.
Learning to fly a complex aircraft isn't hard at all. Just remember to retract the gear after you take off and please, please extend it before you land. And you set power by first setting a manifold pressure setting and then adjust RPM for cruise. The 172RG is simple enough to fly. Just remember to get that complex signoff so you can log all that time as PIC. Shouldn't take much more than an hour.
As for the time to get the commercial SEL, learning the maneuvers should take around 10 hrs or so, as long as you keep at it. Everyone wants to rush through the lazy-8s. Remember that they are a slow maneuver.
-MJ