I'd say the 6ch radio is the sweet spot for RC. Barely more expensive than a non-frills entry 4ch, the 6ch sets have a bit more programming and mixes which will help out down the road. You can still take a high-end 9ch system and fly it with all default settings.

I'd also not buy a new 72MHz radio. I'd be OK with a used one since so many are being dumped on the market they can be had for a bargain. I also favor the Spektrum 2.4GHz over the Futaba but all my FM gear was Futaba.

I fly the JR X9303 now and the son has the Spektrum DX7. Our 72MHz stuff gets left on the shelf these days.