Use a OS 46 LA engine instead, you do not need that power and it is considerably cheaper. Also, go with the kit for 2 reasons:

1) If you crash it or damage it in any way (it WILL happen) you will ahve a much better chance of being able to fix it.

2) All planes except trainers assume that you have some prior building experiance. So, if you get an ARF, then on your next plane it will be even harder to learn how to build.

Trainers are traditionally the easiest planes to build, especially the Kadet LT-40. I was in the same boat you are in, "Can I really build this thing?" Trust me, it's not that hard. Besides, building is half the fun, not to mention cheaper. Watching a box of wood turn into a flying machine is simply pure self satisfaction. Remember, regardless of what you choose, HAVE A EXPERIENCED PILOT HELP YOU LEARN TO FLY!