How Shopify collection filtering works, and where it stops
Filters are configured in Search & Discovery, not the theme. The exact limits, how filters appear in the URL, and what to do when you hit the ceiling.
Product data
Articles tagged Product data.
Shopify metafields, tags, or an app: which one for what
Tags for operational grouping, metafields for attributes customers see, apps only when you need behaviour. Why using tags as a database gets expensive.