Hi Diane,
before "killing" the old machine do two things from all of your InDesign CS4 documents:
[1] Export them to the IDML exchange format
[2] Export them to PDF/X-4 with no downsampling of images and no conversion of color
You can do this automatically in batch with a script by Peter Kahrel using InDesign CS4:
https://creativepro.com/files/kahrel/indesign/batch_convert.html
Note the option:
[ x ] Include subfolders
Why PDFs? If you open a CS4 document in a new version of InDesign there will be some changes in text reflow.
So you need the PDFs at hand to compare the results. Why IDML? Could be that there are slight corruptions in your old documents. IDML could sort this out. Not all, but some.
Regards,
Uwe Laubender
( ACP )