My approach would be to start by separating the straights, circular and interchangeable needles. I would then start separating the straights by size. As I was working on the straights I would look for 6 to 12 sets that stood out, color, material, unique in my eye for some reason. These I would place in a clear glass vase. Fill the vase 1/2 to 2/3s full of rice and push the needles into the rice. This would be a display of the gift from your grandmother and look like a flower arrangement.
For the rest of the straights I would knit a "scarf" 6 to 8 inches wide in stockinette. I would then slide the needles through the scarf for hanging on the wall. Depending on the number of needles they could be by color, manufacture etc. If you have to many to hang the scarf could also be used to roll the needles up for storage.
A similar "scarf" could be used for circulars and DPNs.
I also use a fishing tackle wallet to store circular needles and notions. Think a small soft-sided 3 ring binder with zip-lock bags inside. They come in different sizes and with different style inter-pouches. An example can be found at.