Hmm ... If your piece is already over 50 cm by the time you get to that part of the pattern, my first thought is to re-evaluate your guage.
inc 1 st at each end of next and every foll 4th row (in st st)
I interpret that the same as you do...
-Knit row - inc @ end
- (1st) purl row
- (2nd) knit row
- (3rd) purl row
- (4th) knit - inc @ end
As far as the sleeve being lopsided ... increasing on the same side does make it lopsided. I made Kyoto a while back and it required incs on the same side; it was the V-neck part so it made sense. What section are you working on now?