Despite much practice, I simply can't play right hsnd chords in bar 5 accurately. I would really appreciate any work arounds eg. is it acceptable to leave out highest f after first playing? Any help would be greatly appreciated. Any exercises to help with my span would be eagerly tried also!
For a technical solution that does not involve leaving out notes: keep your hand relaxed, this more easily allows the fingers to stretch.
You might also try rotating your wrist clockwise slightly: place 1 and 5 on the outer notes of the chord (the F to F octave), when you rotate the wrist, you might find that fingers 2 and 3 can more easily reach the A-flat and B.
A teacher would be able to help with this. Try to find one with at least a masters degree in piano performance. This better ensures they can give helpful technical advice. Czerny's Op. 802 has exercises for greater extension (No. 16 and on). http://imslp.org/wiki/Praktische_Finger%C3%BCbungen%2C_Op.802_(Czerny%2C_Carl)
If you find it's still not possible, leave out the lowest F's in the right hand. The top voice is important, and the lower F is just a doubling of the top voice).
Bar 5, I would leave out the bottom f in the right hand.
If you can, to make it reachable, play in the centre of the two notes; a and b, with your index finger.
Fingering for that chord would be:
Play the top f for the first dotted semiquaver and demisemiquaver, then the bottom f for the second.
I think these are acceptable. However, there will always be someone that thinks you can only play it like the original.
If you are struggling with a lot of the chords I think you should visit a piano tutor, arranger or conductor and get their opinion.
For stretching your span, try playing chords that are just within your capabilities and hold them down. Then, whilst the rest of your fingers are sustaining the chord, lift each finger individually (one at a time) as high as you can off the key and then firmly place the note back down again. Playing (in your case 'relatively') big chords is about hand strength to keep your fingers in the right place as well as stretchiness between the fingers.
Hope I helped.