Hi Matthew,
Kentico uses the basic SQL DB Engine features, so the Web edition should be enough for you, unless you want to use other SQL Server features, e.g. clustering, data warehouse, analysis services, etc.
Please note also the Scale limits for Web edition which I think should be enough for your needs.
This document can help you https://docs.microsoft.com/en-us/sql/sql-server/editions-and-components-of-sql-server-version-15?view=sql-server-ver15.