If I use AES (System.Security.Cryptography) to simply encrypt and decrypt blob or memo fields in a SQL server, then where do I store the “Key” and “IV” values on the server?
Segregating your web server and db server would be helpful here. You want to lock down access (permissions-wise) to your encryption keys, and keep them in memory as SecureString. Can't do much more than that. Choose strong passwords and follow up-to-date security practices.
Here's a good post as well Where to Store Encryption Keys MVC Application