personally i'd skip the citra or go very very lightly. it isn't a subtle hop. it'll likely take over your beer and hide the cuke. between flavor and aroma additions, i'd keep it under a third of an oz for 5 gallons. also, don't use citra for bittering. go with something cleaner.I am thinking Citra will bring out some really nice qualities and still let the cukes shine through.
as always: IMHO, YMMV, caveat is emperor, etc...