from the pictures i got two major things that i thought about when i first saw it. 1) you need some sort of gutter system above the planting area or you could have some problems with a bad snow fall and or water buildup. 2) do you want to hide the stone veneer on the wall next to the walk way? i would think annuals would be the easiest, the only draw back is replacing them every year. if you are looking for plants. another alternative is a mexican beach stone as a drip line that would add a nice touch and double as a drainage system. Than i would place a small perennial bed on the outside of the walkway to frame the walkway to make the design more 3 demensional rather than a straight line.