Hi Mo, I usual have about 6-15 or so sequences/timelines per project. Some are nested. Most are made up of tiff animations, 3k and 4k drone footage, 3K and 4K (25 and 50 FPS) go pro footage, and standard 4K footage at (50FPS, 150 mbs). Sometimes I add scrolling text.
I also use green screen layers, slow motion, optical flow and play some clips backwards - most with color correction...thus the need for proxies and/or rendering the timeline even with a fast GPU and CPU. (I just started using proxies, but I prefer rendering previews.)
I have seven partitions on 6 hard drives. The SD drive is divided into a C for applications (400GB), and D (600GB) for video previews and the media cache. I also have started putting proxies and video previews on 2 other SATA Hard drives. HMM. perhaps changing the scratch disk mid project to a new hard drive on a couple projects caused some of these problems?
I finally have most of my important sequences now rendered (between Christmas do's). The rendering seems a bit faster with this new upgrade.