Outputting Assets Instead of Entries
Since there is several moving parts here, i'll make a few assumptions.


You got a list of some kind with the product images and their containing metadata.
Your product image filenames have a consistent naming scheme. Something like product-condition1-01,product-condition2-01, product-condition2-02
You are able to write a couple PHP scripts and/or some frontend code that uploads your images, and then creates an list with the returned fileIds and the matching image filename. Take a look at AssetsService and the uploadFile action in AssetsController. For the uploading part, you can probably make a simple JS snippet that loops through the file list and uploads them.
After you got that list, write a script that runs through the product list (an CSV or something), and replace the placeholders matching your image filenames (product-condition-xx etc.) with the previous fetched fileId(s).
You will then end up with a comma-separated list of fileIds in your CSV fields, which Craft expects to able to relate the Assets to the imported Entries.
Import the entries with Import.
List the connected assets in your entries template the normal way.


I have not looked into how to save field info for Assets, but you can for sure make fields and then add them to the field layout for your Assets Sources.

(Not sure I understand all the conditions, but I think my outline should work pretty well for your case. Not able to comment yet, so I could not ask any questions beforehand. I'll update my answer if you add some follow-up information).