In my experience, it will cost you more to build a kit than to buy the ARF version. Once you've added up the neccessary tools, glue, covering etc. it will be more, so if you want to build a kit to save money, I don't think you will. Of course, the next kit will be cheaper since you now already have all the tools, extra balsa etc.

So, you need to make that decision based on what you want out of it. There are numerous threads about ARF v.s. kit building and how most people feel more pride in their built models etc.

My first two planes (trainer and low wing trainer) were ARFs. My third plane was a kit (Somethin Extra). Personally I do find that I have more pride in the SE, however, I don't know if I would want to learn to fly on a kit built model. I might have been too nervous about crashing it given the number of hours it takes to build it.

I would suggest starting out with an ARF and then while learning on this start building your next plane as a kit.

Both the Evoloution and the OS AX are good engines. The OS a little more expensive. I have the Evolution and found it to be a good engine. I don't think you can go wrong with either engine.

-tychoc