How long should a Shopify meta description be?

Shopify SEO fields
FieldRecommended length
Meta title50-60 characters
Meta description150-160 characters
Product titleUp to 70 characters
URL handle3-5 words

Does Google always use the meta description?

No. Google rewrites the snippet when it finds page text that matches the query better. A precise, keyword-relevant description is used more often than a generic one.

Should the URL handle be changed later?

Only when necessary. Changing a handle changes the URL; Shopify creates a redirect, but repeated changes dilute the signals the old URL had accumulated.