I built one of those GP extra's years ago. It was a great flying plane. In fact at the time it was one of the best I had ever flown. It was a little heavy though compared to todays standards. Typical of the older kits. If you just want to fly around and do some advanced aerobatics, it will be fine. It was not designed to 3D. It was designed before that era. The ailerons are too small and it is too heavy. I had several different engines in it, but a Super tiger .60 was my favorite. a good ,90 four stroke would be a good choice. Enjoy the plane. You will like it. Also, good to see you wanna build. Not much of that anymore.
Also, your list of planes is perfect. The Kaos before the Extra will be good.