Here's what I've learned from my experience with my pair. I hope it helps a bit.
1) It's absolutely possible that you'll get a troublemaker with terrible litter habits, so be prepared for that possibility. When we got Hannah, I freaked out and wanted to give her back because she was crazy hyper, didn't have great litter habits, and got into *everything*. Otto is quiet, calm, is incredibly clean, and doesn't do more than lay around the house, so I was really afraid to end up with a crazy bunny. Now, I adore Hannah and I'm so glad I kept her. She is crazy, and has a lot of energy, and sometimes gets into things no matter how well I thought I bunny proofed, but she's so entertaining and snuggly that I forgive her. Her litter habits also improved a lot (once she got over marking a new house that contained another rabbit). She destroys more things than Otto, but over time I've put their pen on a rug and she's mostly left it alone. In her case, having a calm friend and plenty of space allowed her to be less anxious and less destructive than she was as a single bun. Not that this is always the case, especially for a bun who is just destructive and not anxious like her, but having a friend can give an active bunny something to do with their time other than chewing and diging.
2) Is the HRS going to hold them for a time and bond them for you? Or are you going to date and then bring them home to bond yourself? Either way, there will be an adjustment period and it will be stressful for you (at least it was for me) but you'll get through it. I'm of the opinion that just about any bunnies can be bonded with patience. As long as they're not at each others throats going for blood (and of course that's the point of the dating, to make sure this doesn't happen), you'll get them bonded. If you only date and then do the bonding yourself, be prepared for at least a month or two of sessions. Mine were pretty good together from the start, but it takes some time for them to get comfortable and learn how to read each other, so don't get nervous if they need some time.
3) Most bonders switch them between cages every day or every couple of days so that both scents would be all over both cages. I couldn't do that with mine, as Otto's cage wasn't super secure (since he doesn't ever try to escape) and I knew Hannah could break out of it, so she had to stay on her side and it worked out fine. Even if you're going to build a whole new cage for them to share, having them swap sides will get them used to living with each others scent. At the end of the day, bonding is all about making them think that this strange new bunny is a part of their "warren" whether they like it or not. Haha
4) Bunny personality around people isn't always a good indicator of how they will be with other rabbits. Otto is laid back and nonchalant around people and turned out to be the same with other buns. Hannah is sweet with people but bossy, and she is bossy with other rabbits, but at the same time she loves them and isn't mean on purpose. She was absolutely obsessed with Otto at first (still sort of is) and while she can be overbearing to him, it's obvious that she was really excited to have a bunny friend and just wanted to love him. Not every diva will hate having a new rabbit around
5) There isn't just one bun for everybun. We decided that we really wanted a second lop, so we really focused on lops. We were lucky that Otto was good with every bun we put him with, so we could choose which one we liked best, but even a fairly difficult bunny will probably get along reasonably well with a variety of rabbits. If you don't like any of the ones she likes, just wait a while and look again later. If she turns out to be very difficult and really only gets along with one other bunny, then you'll probably be so happy she's not beating the new bun up that you'll take him home right away :-P