Title and caption

FWIW, I would find out all the metadata fields that are exposed by your web site for SEO. No need to duplicate information in Caption if it will already be included.

As to content, Title to me is always important as it conveys to the viewer that the maker envisioned in presenting that photo. Caption is a way to extended the makers personal feeling about this image. Maybe something about where it was and what attracted the maker to it. If there is any location,history, ancedotal information that can add colour, it will make the image more attractive.

I don’t know the answer to all of the questions, but a couple of things are important to understand.

The metadata fields in Lightroom Classic are based on the IPTC standard, so there are some industry guidelines for filling them in no matter which software you use. The IPTC Photo Metadata User’s Guide has their guidelines for Title and Description/Caption. It’s best to keep it simple, because if you export from Lightroom Classic with metadata included, that information can be displayed on a very wide range of web sites, web browsers, and mobile devices, and some might not show all the formatting and punctuation you use. Avoid including exotic characters, line breaks (carriage returns), tabs, multiple spaces, HTML code, etc. because they might not be used on some devices or viewers. Also some fields limit the number of characters, according to the guide above.

The other important thing is to study how your e-commerce site handles Title and Caption. For example, on the website I use, some templates show both Title and Caption under the thumbnails on the gallery page, some only show one or neither. Individual photo pages can show both. I had to run a few tests to understand how they handle them, and that is probably a good idea if you don’t know.