I don't know where you are in your implementation, but I thought I'd make a few suggestions. With all that grass and the slope, I'd look at a plan for raised beds and retaining walls - create different focal points. If you do the work yourselves, it can be done fairly economically (I speak from experience.) As for plants, I'd focus on some good layering of easy to care for shrubs, grasses, perennials and ground cover. A repeated use of the same plants can create harmony, while keeping the care manageable.
