I can answer some of the above:

Little planes are all twitchy. That's just one of the tradeoffs for the small size.

The Champ is well proven but may not have the durability you are looking for. The mini-super Cub would probably hold up better.

These little 3 channel deals won't train you for say a serious aerobatic plane, but any stick time is progress. You won't learn to land right for glow powered planes, you won't learn to manage your speed the same or recover from stalls, and you won't be able to do any aerobatics beyond small loops and maybe a stall turn. But to take 30 minutes to go out to a field and enjoy tooling around, they'll be fine. When you're in a position to invest the money and space on a more serious plane, you'll at least know how to make turns and read how the wind is affecting the plane. If you're talking about going to more serious park flyers, you're starting in the right place to learn orientation so that you can manage models with no self-righting characteristics later.