I can’t begin to answer all

I can’t begin to answer all your questions, but when dealing with a PC that chokes under large video files, learn how to create proxy files. Premiere and Final Cut (Mac only) have functions that make the use of proxies simple. Proxy files are just low bit rate copies of your main files. You edit them as usual but then use the NLE to replace the low bit rate proxy with the high bit rate file. Google that term “video proxy files” and you’ll find out a lot more.