I want more time and attention payed to character creation and development as well, but I don't feel the same as you do concerning well, everything you've stated.
1. She's obviously very knowledgeable regarding all kinds of tech primarily spacecraft. Her knowledge is what feeds her, and I imagine that living in such a desolate shithole dreams of flying anywhere else sit at the front of her thoughts.
2. The mechanic thing. Again, food, years of scavenging, natural capacity for it (just like dear old daddy Solo?)
3. This movie is changing things most apparent of which is the force itself. I like the way it's portrayed here better than it was previously, because the force feels more present, vibrant, and alive; here the force isn't merely observed in the actions of those hero characters we're rooting for, it's almost it's own character. I'd like to say it would make more sense if she were able to wield a saber more easily than Finn did, but his indoctrination at an early age into the the baddies could easily have put him a place to train in melee combat. Maybe then Rey should have been less capable with a saber; she was on the back-foot for most of her fight with Kylo, and if anything if there's question of why she could fight him, umm the Force. Easy. "Training" in this series looks like it means bringing into focus what's already present. Maybe the force gives natural talent to moments of athleticism and action; in episode 1 punk-ass Anakin could do what no other human could do and pod race. Force. Easy.
So why is she able to battle Kylo? THE FUCKING FORCE.
4. She needs flaws, plural and deeper more meaningful ones, but to say she doesn't have a flaw at all tells me you need to watch again and this time actually observe instead of coming straight to 4chan like every other asshole to gripe like a child. And moreover was Luke Skywalker developed to any greater extent in episode 4? No, he wasn't. In fact, they're almost carbon copies of one another.