I've set bc on top of a cake before, and I've set small ri flower on the sides of a cake, but never tried to set bc on the sides. I know you've already told me to start at the bottom and work up so they can support each other, but how do you get them stuck in the first place... I mean, I'm thinking that I will squish out a bunch of bc where I will be placing them, but then how do I get them to attach? Won't I need to kind of press them into place? I'm afraid they will crumble....

Yes, you can pipe BC on the back of each rose before placing them.
Yes, you can press them into place,
No, they won't crumblethey will have been air dried for almost a week before you use them... you'll see. Just handle them carefully because the petal tips are thinner and more delicate. You will break or slightly crush a few tips, but don't worryit won't be noticeable, especially when you add leaves.
BTW, you don't need as much icing as you'd think to attach the roses because the leaves will also help to keep them stuck.