The nesting discussion is another matter, has certain advantages in some cases, and not in others.
The real issue is why these projects fail to open after they reach a certain size. But your experience has raised the question, why are some so much bigger than others of similar content?
And all the coaching about saving your work frequently is moot when the work you successfully saved still won’t open.
My experience was that as my project grew in size and content, the .veg file became very slow to open, before it finally failed at about 70% of loading. This was true for both the .veg and the .bak file.
And I have a well appointed PC with quad core i7, 24GB ram.
I still have a large project unfinished that hinges on my solving this issue. So let me know if you find out anything by posting here. And good luck.