Hey Danny looking like you are making good progress. The drainage grates are a great idea.
Are you sure you want to use river stone for the walkway area? What do you think about some sort of flagstone, limestone or bluestone pieces? They would give you flat stepping stones to make the walk easy and stable. You can set them right on top of gravel or gravel and fill in around them with a little additional grave to make a pretty nice, easy to walk on, walkway.
A few years ago I made a path around a shed that connected up to a grape arbor, and a stone staircase that goes through my woods. I cleared the ground like you have, then I set down sand and set small and medium stone 'slabs' on the sand. It was filled in with pea gravel between the 'slabs' and I planted grass and flower beds adjacent to the path. Its held up without any problems (except the occasional weed growing in between the stones). And it is easy to walk on. I used bluestone that came in random sizes with the biggest pieces being 12" by 18" and the smallest ones being about 4" by 6". The hardest part was they were random thicknesses so some had to be "dug" in and others could just sit on top of the sand.
The picture below is taken at the bottom of the staircase where I built a landing out of the bluestone. The picture is looking up the stairs, there are 4 'sets' of 4 to 5 stairs between the base of the hill and the top of the stairs, each set of steps has a small flat landing before you get to the next set of steps. When I was done, almost all the dirt in the photo below was covered with the bluestone.