You want plants that can stand reflected heat. If this area will not be irrigated you may also want drought tolerant plants. Visit a local nursery (not a big box store) and ask what they think would be suitable for this space. Off hand I suggest LANTANA, a 2-3' tall and wide semi-evergreen shrub which has flowers of pink and yellow, or orange and yellow. Very dwarf evergreens with colorful foliage would work too. Cultivars of Juniperus horizontalis or Chamaecyparis pisifera offer relatively carefree year-round interest.

How many you need depends on their mature spread. The lantana, for instance, should be planted at least 2 feet from the edge of the driveway, a building or a fence/property line, and each plant at least 2 feet from another. Initially more rock will show between the plants, but be covered up as the plants grow. If you want the rock to always remain visible place the plants farther apart. I prefer a staggered planting as it looks more natural to me. Grouping plants in odd numbers also looks more natural to me, but it's not an absolute rule.

Thank you so much. These hollies were 8-10' tall. They were pretty with all the red berries, but would fall on the driveway. Their roots were going under the driveway and making it crack. Will get a new driveway when I get the beds near it finished. I did have a purple trailing Lantana at the edge of the bed and driveway. I loved it, but it grew 4' over on the driveway. I did get to save some of it and it could go around the rocks. The rocks will be higher and farther away from the driveway. The Lantana will die back here and would need to be cut back after winter. I may look into the dwarf evergreens also. I am 74 and like the idea of growing rocks!