What a good tip. I like the idea of getting her used to your scent. So cute how she is now bonded in to your fiancé. I would sleep with a toy rabbit for a few days, and put that in my bunny's cage. Same sort of idea, but my bunny began grooming the toy bunny.
Regarding when to get her spayed, it really depends on your vet. Some are comfortable with spaying females when they reach sexual maturity, while others prefer to wait unit 6 months.
Just a note on same sex bunnies getting along. It can happen, but it can be challenging. Their is a hierarchy within the bunny world. One among the group, and then another within the same sexes. Males fight for territory of mating rights, females fight for territory for safer birthing areas - it's in their instincts so though spaying can temper this, they can still be a challenge to bond.
If you go to a pet store, my guess would be that the rabbits would be young? Unaltered? So even if she finds a "passive" male ore female, when that baby bunny reaches sexual maturity, a whole new personality can emerge. You may not know if that baby bunny is going to be a dominant rabbit or not, it'll all be in the hormones, and those don't happen until around 3- 4 months.
Have you ever thought of going to a rescue group or shelter/humane society? Many are experienced in bonding, and can help you through bunny dating. I know that when I worked and volunteered at shelters, people would bring in their bunny, and I would bring out a bunny and see how their bunny reacted. I could read the body language and tell if their bunny would be okay with a dominant bunny or had to have a passive bunny. I could then go and find a better choice - one that would more likely succeed though a bonding process.
If you do decide to go the a pet store and pick-out a baby, you will just have to be very careful when you get home, and make sure to go through a bonding process, and then be prepared when the baby reaches 3 months old to watch very carefully for aggression, and if it's a male, you'll have to separate them before that, as females can get pregnant as early as 3 months (one good thing about most shelters, at least in the US, is that many times the rabbits are already altered.)
Either way, I do think having two rabbits is a great idea. You just have to go through a bonding process to prevent fighting (they can seriously hurt each other)
Most really do crave companionship, and it's wonderful to see to bonded rabbits playing, sleeping and grooming each other. And I know some people think that their rabbit will ignore them. I don't have that problem at all, if anything, when I pet one rabbit, the others come to join in, and we all cuddle!
Regarding when you move. Moving can definitely start a whole new routine of marking - leaving poops everywhere, but it if you start to litter train now, it can only help cement in good habits. Waiting doesn't help, and if anything, bad habits can start to cement in.
Well, lots of choices! Congratulations on your new cutie pie! You sound like you are dedicated to making her happy, and care very much for her. Keep us updated on litterbox training, bonding etc. and we're here if you need any advice or just want to share your experiences.