I really think the fruit question is something you will need to experiment with yourself. Only your body can tell you what or if fruit will work for you. Atkins himself stressed how individual we each are in terms of our carb tolerance.
So experiment--and keep experimenting, because as your body adapts to the new diet regime, it's sensitivities may change. What caused you problems early in the diet may not later, or vice versa.
Also, as for gaining the weight back, if you return to high carb eating habits, you will likely regain weight. Though your sensitivity to carbs will change the longer you're avoiding carbs, I don't think the problem typically goes away. The basic body chemistry remains a constant: as long as insulin is in your bloodstream, you won't be burning fat. As your insulin resistance reduces, your blood insulin levels should be reduced as well, but I don't think it ever goes away.
Good luck!!!