Joining of Octaves
Don't practise starting from loud dynamics, start playing it softly. Just ignore the dynamic marking first and increase on it eventually.
Choose to sing out the top or lower note of the melody. Top note is lighter and the sound is more free, comparing with bottom note which may sound rigid when its played loud. However, singing out top note is harder because the 5th finger is usually weaker. Make sure the bridge on knuckles is strong and 5th finger must be firm on tip, don't collapse when playing. Listen! The top notes must have a healthy sound, not a half dead tone.
Whole arm must be very relaxing especially for a pianist with small hands, since when stretching out for the octaves, the hand is naturally tensed up. So practise slowly in the beginning to avoid putting more tense.
Always adjust arm to higher/lower position and let the arm follow the fingers movement. It means when reaching out to far notes, move the arm to the side so that its lined in a straight line with the fingers.
Use strength from upper arm to play louder notes, because upper arm can have more strength, lesser tension and it will produce a richer and deeper sound.
Use 5-4 or 4-5 fingering where it is marked and work it out even if your hand is small. Practise in small segments, either 2 notes apart, 3 notes or 4. Octaves going downwards is easier to join than upwards. Try to use 5-4 or 4-5 fingering on octaves going upwards if you have big hand. If not, its an unfortunate disadvantage but nevermind
To make it more legato between octaves, try to feel consciously about imitating the movement of a snake's gliding on the surface of keyboard, never lift fingers higher or a little jump between octaves.
To make it even more legato, give more shaping motion, because shaping eventually works a miracle to make it sound more legato.
On bar 61-62, last 2 bar of the Variation 3, try to grab more on the tip of fingers, like trying to lift something up gently using the tip of fingers, in order to produce a more singing tone. Be careful about stiffness.
Pedalling - cannot pedal deep because it consisted mostly of 2 consecutive notes which are not from the same chord. Pedal very shallow only for every 2 notes. Practise on pedalling so that the sound is also not broken.