RE: What is a good starting plane for 3D and aerobatics
I would work on your set up skills and use the Stick for most of the practice stuff.Its more capable than you think,so play with all the adjustments.I'd move to the Showtime after that,but not use the 91,use the 52 if its any good.
Or get a 90 size Showtime and use the 91 or the OS 120 that you have.The bigger showtime will make 3D look better with its light wingloading and bigger presentation.
Once you get very comfortable with the Stick,the Showtime will seem like a real easy and high performance aircraft,which can used to advance your skills to high levels.