My experience is in electics and sailplanes, not glow. Working from that background I know way too many people who started on their own and are now flying lots of planes who received little or no help, beyond the forums.

I can certainly see the wisdom of an instructor if you are starting in the glow world. Between engine set-up and tuning and the higher speeds, weights and wing loadings, there is a lot more going on and a lot more damage that can occur if something goes wrong. Hitting something with a 16 ounce 20 mph rear propeller foamy is quite different from a 60 ounce 40 mph balsa object with a fast spinning prop on the front.

On the 3 channel RTF electics, basically you charge, plug in, hit the throttle and go. The motors don't stall and they don't run lean so the motor knowlege/training pretty much goes away. And most of the electric ARFs either come with motors or give you specific recommendations so figuring out electric motors has gotten a lot easier.

Once you get past the power systems they fly pretty much the same. Pitch/Roll/Throttle on 3 channel and Pitch/Roll/yaw/throttle for 4 channel.

Since the glow planes do tend to be heavier and faster than the typical RTF/ARF electic, they do handle wind better. I recommend new electric flyers, especially ones training on their own, do their early flights in calm to 5 mph and no more. One you get good, 10-15 mph winds can become a fun challenge.

You can certainly learn to fly on your own with the small electrics or gliders. But frankly it is a faster and a much more fun process to at least get a coach/advisor/friend to help you. And, an instructor is always the best way to learn.