Have you decided which variety to use? Claytonia for example, (virginica) is a very early beautiful little plant. But, although its flowers are lovely, however they are very small. On the other hand, Claytonia siberica has thicker, more deeply veined foliage and it flowers for months.
Procumbens, commonly referred to as Allegheny spurge. In virtually every respect, it is superior to its more frequently used Asian cousin, terminalis is a very aggressive and stoloniferous. This can be helpful if you want to fill in a very large area super fast. The American variety, P. procumbens, is a clump forming groundcover that fills in an area a little more slowly, but much more elegant.
Procumbens is hardy in most areas of the U.S., probably into zone 4, in colder areas it is a herbaceous perennial. In the early spring, when the ground is bare, procumbens puts forth spikes of pink and white fragrant flowers that last two weeks. Soon after the dark green leaves begin show. In deep shade, the foliage remains a dark, luxurious green all summer. The more sun that the plants get, the lighter their leaves are. They will be healthy and productive but the leaves are paler in color, some with an almost chloritic appearance. This is a dappled-to-deep shade plant!
Are there erosion issues with this hill once you kill of the grass? Is it irrigated? As far as quantity needed, will depend on whether you use liners, 4" or 1's, and of course the "budget".
with regards... devildog