I've tried several times to follow your link, but only see a potted plant. Perhaps re-post?

Go to the public library and borrow some gardening books on Rock gardens..that's the first thing that comes to my mind when I look at your pictures. With rock gardens, I wouldn't think that you'd have a lot of plants to buy. Maybe a few six packs of each chosen plant. You'd need to fill in with added gardening soil and compost I would think. Why not take a copy of the picture you posted to a good nursery or garden center and ask for some suggestions. I would think that you would need to fill in the area with gardening soil and compost. Ortho puts out some great gardening books, go to your local book store and look through them, maybe you'll get some ideas from them. Include both perennials and annuals. You will get instant color from your annuals but they don't come back year after year unless you buy plants that reseed themselves, which is my goal for next year. I don't have a slope/hillside to work with though. Posting here will help you get lots of ideas. The gardeners here are wonderful and you'll learn a lot. Most are very willing to share their knowledge and experience. Ask friends/neighbors and relatives to share some of their plants that you like. There's a good book called Pass-along plants that you might enjoy reading and it will be helpful.

What did you end up doing with your backyard slope? Are you happy with it? Pros? Cons?