The bus does go all the way to the ski centre, No23 if I remember rightly. It was running hourly last summer.
There is a good path all along the route you're looking at. There's a few different ways up onto the plateau, all good. The way to Macdui is marked by about 50,000 cairns, it's hard to see how anyone could get lost up there. The start of the path down from the summit to the Hutchison is a bit indistinct at first, it's all scree. Gets better as you descend. The rest of your route is on well made paths. Enjoy.