A six channel radio is going to add retracts and flaps. The Futaba 6exa has plenty of mixing capability unless you want to do something very advanced. V-tail, elevons, flap/elevator, and a couple others are in there. More than the basics.
You've done your research and are more aware of your radio needs. The rest of your plan is excellent.

A kit would easily cost as much as the ARF and maybe more in terms of tools. But you'll be more capable of fixing your airframe after those "hard landings". Not to mention that it's just alot of fun to build. I don't hate ARF's. I even own a couple. But the scratch/kit built airplanes are the ones I'm attached to.