1: No, each leaf contributes to gas exchange; there should never be a "need" to defoliate before first having a reason to do so.
Defoliation, or the removal of leaves, can cripple gas exchange in plants. Specifically, it can significantly reduce a plant's ability to take in carbon dioxide and release oxygen, which are essential for photosynthesis and respiration to occur. It doesn't matter how much DLI she gets; if she can't perform stomatal conductance, it will bottleneck growth dramatically.
2. Nothing is necessary; everything is stressful. Very possible and recommended, don't even worry about fcuking it up, that's how you learn, just make sure you do your homework prior and have the tools ready and at hand for instant repairs, in case needed.
3. If it's an aut,o that's normal, she is just stretching very well, getting a lot of work done in a cycle,