Best overall NEX lens for wedding (mine!) plus "hill" climb?

I have an 5n and love it, as well as 16mm + UWA, 18-55 and 55-210. I'm soon to be married in Feb next year (low fuss + big knees up) so will be getting a close family member to snap some memorable shots, then we are heading out to climb Kilimanjaro as part of our HM. I have been looking at the available NEX lenses and would love to know if there's anything else worth getting that would make that much difference to the stock kit I already have?

1 burning question I have is, is the Ziess 24/1.8 really really worth 4 times the amount of the already expensive but well reviewed SEL50F18...? Focal length apart, do you actually get 4 times the quality and "WOW"?? I wish I could borrow or hire one but in the UK I dont think we do that! Here we call that theft