Some observations from an old guy that's been around the hobby for a while....
Take any plane you want, and fly basic with it, and don't worry about what others are flying or what's up with a guy who would rather win basic five times than compete in Sportsman. I never understood that either but you have to expect it.
The events are fun, and it's more about the social thing than competing. I can tell that you had a good time, so don't pass up the experience if you can afford it. It ain't cheap, but if you are into it, it's no different than a hardcore boating or golf addiction.
40% planes have an advantage, they say, because they present better in the air to the judges. But IMO, the judges will give the advantage to the guys that have invested the most time, money, and effort, into the sport/hobby.
The MXS you have now, with a low rate mix, will be a great plane to get involved with. The 78 Extra is another -- less expensive and time consuming to build than giant scale planes, easy to power and transport, and a great plane to learn and practice with.
Practicing the sequences is actually fun and will definitely make you a better pilot. The trick is to pick the right plane, make it your IMAC plane, and focus on that plane all the time, during practice. Switching planes all the time makes it tough to get really good, really fast.
As popular as 3D is today, a good sequence pilot still gets more respect from more people in the hobby. Jesky, Leseberg, Somenzini, Hyde, Shulman... they all made a name for themselves in TOC and IMAC.
Freestyle has some 3D, but is mostly big sky XA, and that's what judges look for. So there may be a chankshaft thrown into the routine, but it's at the top of a big rolling loop, for example.
Most serious IMAC guys used to build their own planes from kits... Carden and Godfrey Extra 300's were the top shelf planes, and Dalton is another. The advantage of a kit is that you can make modifications to suit your flying, if you know what you're doing.
PAU makes some nice ARFs for IMAC, but the big Extreme Flight Extra 300 would be my first ARF choice. A really solid competitor.
Take this as simply my opinion, because you will find that everyone involved with IMAC has one
Oh, and if you watch the video of Joe S flying the custom Carden Edge, I think you may see something interesting. I won't say what, but check it out and remember it's the first time he flew it.