Hi again!
The image-alt text is meant to help visually impaired people still ‘see’ the image. As for SEO, it has no merit other than training Google’s AI.
With Google Image search, images can be found via data posted on the page, such as the page’s title, meta description, and content. There’s no reason to copy the page’s description into image alt-texts for SEO-reasons, and it could, in fact, be harmful to accessibility if the content is disparate from the image.
Here’s a proper example of an image we did not ‘SEO optimize’ (tautology intended):

From Google’s official SEO guide:
Optimizing your image filenames and alt text makes it easier for image search projects like Google Image Search to better understand your images. [Do] use brief but descriptive filenames and alt text[, but avoid] stuffing keywords into alt text or copying and pasting entire sentences.
Yet, Google doesn’t need guidance to understand images as much anymore, thanks to their rapid advances in visual recognition, which you can test in Google Lens. In apposition, it’s also funny they call it a ‘search project,’ and not a ‘search engine.’
Moreover, how often do you get people to your site via Google Image Search? Any data obtained by SEOs for research (such as the famous Neil Patel), are obtained from unofficial and untrustworthy sources. These SEO optimizers (tau(n)tology intended) tend to build ‘solid’ cases around lies you should ignore. Their motive is exclusively monetary; they’re not there to help you — because they can’t.
Whatever SEOs have postulated about image optimization, it probably came from a gaping hole it shouldn’t have.
SEO utri non-causa pro-causa.
I recommend filling in alt-tags (if you find the time) via the media library in WordPress. The theme, WooCommerce, and WordPress may (should) dynamically update the images on the site to present these to people with impaired vision.
As for your other inquiry: Attachment pages are useless for most sites, and it’s why we default ‘noindex’ on those, which is good enough for SEO; 301-redirects for those help only with accessibility. If you wish to 301-redirect those, you can use our free extension Cord. Pages that cannot be accessed (for example, because of a 301-redirect) will not present any useful information to search engines. Attachment pages have nothing to do with displaying attachments throughout your site, however.