Ideally, Juicebox would allow me to create fields for the table which I would populate and these would appear below the image or overlay it.

Unfortunately, creating some kind of input method for custom fields for image captions (or anything else for that matter) would be a hugely complex task (and not possible within JuiceboxBuilder-Pro whose source is not available to be modified by users).
You can, however, add as much text to an image caption as you like and you can split text into separate lines using HTML line breaks (<br>).
For example, a simple two-line caption would look something line this

Line #1<br>Line #2

The use of HTML formatting within image titles/captions is noted in this FAQ:
How do I add HTML formatting to image captions and titles?

You could use an HTML <table> within an image caption but the caption area is already a <table> (with its own styling) so you might run into problems (although you could certainly try it if you like).
I am not aware of anyone having used a table in an image caption before so, unfortunately, I cannot point you towards any references for this.

If you do add a lot of text to your image captions, then you might need to increase maxCaptionHeight (in JuiceboxBuilder-Pro's 'Customize -> Caption' section) to accommodate all the text.

I hope this helps (at least a little).

Forgive me if this has been asked before: But, is there a way to set up a table of data that is displayed with each image?

I'm a Juicebox 1.5 user. My mom has finally gotten to the point of having to leave her home. And before we clear everything out, I wanted to create an online garage sale for her contacts. So, with each image of an item, I wanted to provide structured info about it.

Ideally, Juicebox would allow me to create fields for the table which I would populate and these would appear below the image or overlay it. Without that, I would just the html for the table and put that in the comments. Are there instructions somewhere on how to do either of these?

Thanks!
Gary