I've been building and flying free flight and control line model airplanes for some 60 years. My RC experience is a couple of buddy box flights. So take my advice for what it is worth. I'd say buy a trainer kit. Building a kit is more of a learning experience than you might think. Most modern kits have the process all laid out for you and you will find that a great help. Once the trainer has served its purpose, you've had your value out of it, you don't need it any more. Sell it or give it away. No need for it to clutter up your place.

I've built a fair number of my own design airplanes. I have found that making up a flow chart of what to do and when is absolutely essential. This is done for you in most modern kits.