To build or not to build?? I am given trainers by new pilots that have moved onto more advanced planes and use them to instruct with. I teach using the buddy box like most people these days. The only thing I require from a student is they buy there own fuel, everything else I provide. I have never lost a trainer to a student while on the box. After they solo I let them use my trainer and TX until they get there own equipment and plane. So far I have only lost one trainer doing that. The trainers aren't prone to crashing, it's usually the students second plane that takes a beating.
Nothing wrong at all with going ARF for a trainer or even a second plane.
I too would go onto the Blue Jay Models site and look at the Joe Bridi designs. Saying Joe designed a few planes is a slight understatement but anything Joe designed is going to be an outstanding plane and I love building his kits.
The DX-7 is an outstanding radio. My only problem with it is I don't set up enough planes with it to know all the little tricks. I have had several old students decide on buying it and all have been happy with the radio. I'm lucky that the DX is so popular in my area and when I forget or don't know how to do something with it there are several go to guys at my field that correct any of my mistakes. I still have a problem setting up the two ailerons with it but it's a me problem, not a radio problem. I use a Futaba and they program differently.
Good luck with whatever you decide on doing.