If I insert more than 320 character in the meta description at the bottom of the product/vendor page where it says Edit Website SEO (see the attachment), will google still crawl the rest of the remaining characters? I could insert the description near the top where it says (Optional) but however it display the long description on the bottom of the website when someone click on that certain vendor. I'm using Impulse theme.
I would suggest sticking to ~158 char limit. This is closer to the real-world pixel length that Google currently tends to favour on desktop (bit less on mobile).
Shopify seems to have changed their field counter up to 320 following the change google made in 2018, but has not changed it back down again after Google switched back generally showing the standard ~158 char size.
Google will crawl the entire HTML, it's more a question of if and what part of the description it chooses to algorithmically display on a given search query for a given search intent.
I would suggest keep to the lower limit, and make the descriptions on topic and reflect the content of the page, while writing them in a way to entice a click. Reason being is that descriptions are really only shown 1/3 of the time as is - and are auto-replaced by Google 2/3 of the time. Making them too long or off topic can cause trigger auto-replacement more easily.