For example if I was doing a 200% upsize I personally would do these in batches and I would start by trying 20 images first as 4K is 3840 x 2160 pixels. After that, and depending on the processing time, I may increase it to batches of 100 if it is suitable.
Also, because of the processing requirements, I would make sure I had lots of RAM, a fast SSD and a GPU with at least 4GB of dedicated vRAM.
That is a massive job and previously I have tried 200, 6000 x 4000 images but it did grind itself down and I found that batches of 20 were optimum.
The other thing is that if you put the animation together first you may be able to use an app like Resolve to upsize the animation ... but the quality may not be the same as AI GigaPixel.