You can double license software and have a non-AGPL license for customers. AGPL is a must nowadays to avoid Amazon and other giant companies like it to "steal" your project and start offering the same thing initially (2-3) cheaper while you are going out of business.
Ianal, but afaik one is required to release patches to the product itself only if product functionality is exposed to customers. If it is internal tool, patches I believe can stay internal. But if you want to offer, for example, hosted solution based on this product - then you are required to release modifications.
