I have been studying mostly the op 10 etudes of chopin for more than a year.Seriously i plan to have a recital to play them all.But with op 10 no 1 and 2 let me give you my story.I practiced it in every possible way.(from sitting high on the bench and playing with curled fingers,to sitting lower on the bench and playing with flat fingers).
I found out that if you have good control of your wrist and forearm and the flesh part of the finger is in contact with the keys then you can have a very good legato,this etude(op 10 no 1) is not that difficult if you manage to learn how to rest your hand and fingers on the keyboard.It is a myth that you need a big hand to play it (the etude is arpegio so with the exception of 1-2 places in the piece every hand can play it if player knows how to relax correctly!).
Sometimes when i study it normaly i stop,let ten minutes pass and study it again this time "flat finger style",i mean i play slowly,and think everytime of the next hit i am going to do(playing with the fleshy part of the finger).At fast tempo it is fantastic.As for the metronomic indication it is 176 the quarter,but after checking the godowsky chopin etudes,godowsky says that 176 cant help the player bring the grand style of that etude,and gives as more logical the metronomic value 160/quarter that the kullak and mikuli edition has.
As for no 2,you have to learn how to let the hand drop naturally with the weight it has in to the keys,drop in the first two semiquavers,raise in the other 2 and so on,once the tempo is faster you play 4 semiquavers with the wrist going down and other 4 with the wrist going up.The trick is not to lower the wrist manually,but do a controlled arm drop,that is to leave the wrist to collapse by each own weight (not completely but mostly).After you master this (slow tempo is a tool that will help),pay attention to the finger action,and to the legato you have to create (chopin says sempre legato,).Caution if you dont allow the wrist to drop by the weight the arm has and you lower it manually,usually within page 2 in the middle you will feel terrible with your hands and feel fatigued and tired
As for no 4, it is not that difficult,if you have played almost all the sonatas of beethoven then i see no reason why you could not play that etude.I agree that the sound you hear on recordings may fake you and make you feel that it is difficult while it is not.So slow practice and you can do everything.
Also i advice you to get the godowsky editions,it has many exercises for chopin etudes,and try to play some of the transcriptions godowsky did on that etudes,after you resume playing the chopin again you will see that you can play them way better.
Topic: Chopin's Etude #4 - how difficult is it?