Downwind runs always needed more throttle, but thats par for any plane to one degree or another flying slow.
Hummm, could you explain what you're referring to? When you're flying with the wind, your groundspeed will be higher, so you'd want to throttle back if you're trying to keep the plane from getting away quickly.
As for the cub not being a trainer I couldnt think of a better plane to learn on. It will teach you all sorts of skills that most new trainers wont that will stand you in good stead for later models, like the P51, some pattern ships, etc.
Definitely. I still recommend a conventional trainer for initial RC training, simply because the total newbie needs just to figure out the basics of keeping the plane properly oriented and working the controls (without worrying about the plane wanting to ground-loop on takeoff or snap roll in flight), but once that hill is climbed, something like a Cub is an excellent idea. I learned how to "control" an RC model with my trainer and Tiger, but the Cub taught me how to "fly".