1) Based off today, bringing my bunny home from the vet, male rabbit urine smells awful! I have no experience with how a females urine smells. No fear though, if you buy a good, absorbent litter (I use CAREfresh), and you change the litter pans often, the smell will not bother you.
2) I have a neutered male bunny, who has not humped anything, but I do think it depends on the rabbit, about 7 years ago I had a neutered male, lop, and he still humped (not frequently though). But, some females have been known to hump as well (definitely not as frequently as males) ** this is based on experience from a friends rabbit
3) I have only ever had male rabbits, not out of personal preference, but just simply fell in love with the rabbit. I truely believe you need to meet both bunnies first and pick based on personality instead of gender. If you are planning on getting them spayed/neutered (or if they already are, such as from a shelter), both male and females are generally tame and similarly behaved, but each rabbit has individual personalities, which is more important than boy/girl.
Hope this helps, good luck picking out your new forever friend!! =)