I think the 28" is "standard", I am 5'5" with long legs and ride quite long, and have the 28" synthetic version of them on about the 5th hole up... so plenty of room for adjustment. If you have long legs for your height maybe get the 32" - but otherwise I'd say 28" would be fine.
Im sorry, I have no idea!The bates leathers were 2nd hand, and I have them on the top hole to jump, so they are just borderline right...when I bought the wintecs I had a blonde moment and just asked everyone in the saddlery what they thought! They guessed right..
Bought mine from Frogpool, they do good guesswork!