That has to be the most solid answer in the history of forum posts. I really hope you enjoy writing.

Hands together vs. hands seperate:
What I usually do, is just get the fingering right for both hands, memorize perhaps 5 measures, and just start practising hands together. This may be the cause of many passages which are uncomfortable to play, in all of my pieces. I never even tought about how it should feel easy, I was pretty contend with just beeing able to pull it off. That is why I figured I'd try something different this time, and I believe it is working. I am also not in a rush to memorize this, I have two other movements to learn first. They do look easier than both the first and last movement, so they should not cause any problems. If I can overcome most of the technical difficulties of the 4th movement at the same time, great!
Chords:
I am not entirely sure how to play chords as easy as one should. I just move my fingers in position and push down, I guess. If you could elaborate on how to play these correctly, it would be great!
Lateral shifting arpeggios inwards:
Your explanation, well, explains alot. Also, my thumb seems to automatically reach for that last note when I'm descending with my right hand. That is making the motion tense and forced, maybe I just need more wrist motion. I will isolate the problem and just do some more descending arpeggios, taking all your advice in consideration.
My techical issues causing unevenness:
I've uploaded an excerpt from the score. This is the part my right hand is looping on my recordings. My markings in red is were the unevenness occurs. There is my 4th finger, the big stretch of the four notes, and the descending lateral shift all at once in succession. Maybe the anticipation of the upcoming lateral shift is what is making my thumb tense and my playing weird.
Sonata recordings:
I listened to some samples from the John O'Conor collection, and it did sound great. Different, but great! I have the impression that most people (maybe just the youtube-mob, I wouldn't know), tend to like the first version they hear the most. Was these the first recordings you heard, or did you hear a lot before "settling" on this one? Slightly off-topic perhaps, but interesting nonetheless.
Anyway, I probably will videotape some of my playing asap. It's pretty hard to pay attention to every little detail while you're playing, it would be alot easier to analyze a video. When(/if) I get something recorded, I will upload it here!