Upscaling images. How big can a CDR file be?

I've just completed a book (A5 size).  Images are 300dpi.

I've been asked to produce a Coffee Table version, approx. A4, that's twice the original size.

Some of the images will need to be upscaled to two to three times their original size, resulting in a resolution of 100dpi.

I have a few options which I've researched and tried but am not sure how to proceed.

1. To lock in all my grading, effects, etc. I export my images as Tiff, open them in ON1 Resize, which does a nice job of making them bigger while retaining 300dpi resolution.  I import those images back into CorelDraw.  They look great, but the average file size of each is approx 10MB, whereas the original size was 1MB.  Which means my CDR file will be enormous, maybe 1GB in size.

2. I upgrade to CorelDraw 2020 and use the new Artefact Removal and Upscaling options.  This retains the 300dpi and gives me a nice image.  But, again, each image size adds about 10MB to my CDR file size.  And there are over 100 images.

3. I import the ON1 enlarged file (300dpi). I place my original file beside it, but scale it up to 100dpi. I make sure my 'View' setting is at 'Normal'. Amazingly, the 100dpi looks only slightly more pixelly, and that's zoomed in beyond 100dpi. At 100dpi, it's hard to see a difference.  So now my CDR file isn't any bigger.  But how will it print commercially?

4. I haven't downloaded the trial of CorelDraw 2020, but I presume the result will be the same as 3. above if I try an A/B test.

5. Because 100dpi looks fine, I could resample the original images to 300dpi.  Using bicubic?

6. Most of my images are 400dpi scans.  I don't have access to the original prints anymore, and extensive grading, effects has been done on the scanned images.

So, my questions are...

a. Given that my images look fine at 100dpi, will they print fine commercially at 300dpi?

b. If I have to resize and retain 300dpi, resulting in a huge CDR file, how big can it be without crashing, grinding my PC to a halt?

c. I could link the resized images to keep CDR file small, but it's hard to judge resolution and sharpness with the low-res link image.

I'd really appreciate any suggestions and workflows for this situation.

Thanks in advance,