If I'm reading this right, you have the same performance problems as I do with the project.
I have gaps and unused files because I was having such a hard time editing with the buffering/freezing that I never got far enough to use my remaining clips / fill out the project. I'm editing 2160p60fps clips because I want 2160p60fps output.
If I ultimately want to author in 2160p60fps (3840 x 2160 @ 59.94), am I better off exporting all of my source video down to something preview size (e.g. 1024x576), designing an entire video using those, then going back and painstakingly chopping up the actual source video to align with the clips I made in the first "preview sized" project? Does that make sense?
Thanks again for the help and for taking a look! It's a bummer that it seems to just be too much for Video Pad to handle. I'm not maxing out my CPU, GPU, or RAM when I'm trying to preview the sequence but it still locks up. I was hoping maybe I'd just missed a setting or something obvious!