Kylo's obviously extremely powerful. He can't stop a blaster shot mid-air, or mind-control torture someone, or paralyze Rey if he isn't powerful. But he also happens to be a complete fucking mess, which means he's prone to being unfocused and unpredictable. It's what makes him strong, and dangerous, and scary, and weak all at once.
I'm conflicted on this point. Everything you've said doesn't necessarily point to him being 'extremely powerful'. This film is interesting in that it expands the force beyond what we've seen in previous films, and we don't have a gauge as to how powerful this actually makes him relative to others. The context of when we see his abilities play an extremely important role in perception one attains of his ability. It opens with the dramatic demonstration of stopping the blaster shot. The mind-control torture on Poe is against somebody who isn't force-sensitive (or we have no reason to believe that he's force-sensitive currently). He freezes Rey and knocks her out before she's become accepting of her utilisation of the force and while she's actively resisting it. As soon as Rey begins to resist him, he isn't strong enough to overpower her in spite of the training he has had and the apparent lack of training (or lacking the awareness of any training) she has had. Later, he fails to stop Chewie's blaster bolt and is caught off guard. I think he's certainly competent in the force, and above average in his ability, but at this stage I think it's easier to argue that he isn't very powerful (capable, no doubt, not certainly not extremely powerful) due to his inability to overpower Rey and his insecurity and emotional instability further hamper him greatly.
Ren's competency is something that, I feel, really requires future material to properly assess, but his competency in The Force Awakens may be difficult to ascertain given that he is undergoing additional training. If you assume he's extremely powerful currently, I think this creates an issue in regards to how Rey was able to resist his interrogation and infiltrate his mind in that it requires Rey (who no doubt will be extremely strong in the force) to overcome a far higher barrier than if he's really not as powerful as he tries to claim and wishes to believe. If you assume he's extremely powerful currently, it does add an interesting aspect to his driving insecurity, that he is terrified he won't be powerful enough to 'live upto' Vader when in fact he actually is (merely in relation to a 'potential' level) and his insecurity is unfounded but furthered by Rey's potential superiority.
Personally, I don't think it ultimately matters whether he is 'just powerful' or 'extremely powerful' and trying to estimate his 'power level' as I don't think it greatly matter or there's enough information to properly assess where he's at (but I do think that if made to choose I would say that I am of the opinion that he's not as powerful as he tries to portray; I definitely was the first time I saw the film, less so the second), I do like the idea of Ren successfully dispatching Snoke after completing his final training being driven by his knowledge that Snoke is merely using him (and as a thought, him then taking on an apprentice [Rey? Unlikely however], but I'm not sure how they'll operate with this and may not go down this route).
EDIT: Also, even beyond all that, we really don't know what way they'll go with the force. They may forego the idea that people are limited or capped by a potential 'power limit' with the force, and that the only separating factor between people may be how quickly they can pick things up due to their willingness to let the force guide them.
She's too nice. Had they written a darker side to her personality in VII, I might be inclined to go with this as a possibility, but she showed no signs of not just being a super down to earth and kind person. I wouldn't make that avatar bet. At worst she'll become deeply flawed through events and choices spurred by her newfound powers, but I don't think she'll go in that direction.
I made posts about this thought recently but the more I think about her character the less I think it's going in that direction.
She's definitely feeding off anger in the final fight of the movie and draws from it while utilising the force, but I do agree that she probably will not become a villain, and I'm hesitant to believe her primary struggle will be with the dark side, mainly because of it being something repetitive (cue "it's poetry"), even if possible.
