Minimum database privileges for Craft front-end?
Short answer, no. You'll want to make sure that your DB user has all of the necessary privileges.

Just because you're not entering your data into the database doesn't mean that Craft isn't writing its own data into the database. There are several tables responsible for handling data which is automatically generated by Craft, and not managed directly by admins.

For example:


craft_sessions records user sessions, to know who is currently logged in.
craft_assettransformindex saves any image transforms which have already been triggered.
craft_templatecaches, craft_templatecachecriteria, and craft_templatecacheelements store data from templates which use the {% cache %} tag.


And there are probably others that I'm missing.

Bottom line... Craft needs to be able to write to the database just as much as you do.