Software systems that need certification or approval

I am a self taught programmer and web developer, planning to become an Independent Software Vendor. I am creating a software for Accounting and Inventory Management to sell in my local market. Right now I am planning to sell some copies of my software so that I can get some money for Bootstrapping, registering and other legal formalities. My questions are...

1. Do my software need any kind of (legal)certification or approval before it can be used by end users.
2. What kind of software systems or (niche)market do need some kind of certification or approval.
3. As I am self taught. Am I restricted to something and lacking something other than highly technical skills or I can create and sell software systems freely.

There are certain situations where you will need to be compliant with certain regulations. If the accounting portion stores CC's it will need comply with PCI requirements for that. You are responsibly for enabling that option. Additionally, if hospitals or other medical areas were to use it, you would want to ensure that everything can be done HIPPA compliant. This is assuming you're in the US, and there are many other things that a company would want to ensure is done before they purchase.

Additionally, if you're going to do this SaaS you will want to make sure that you have certain things done. Like having an onhand SAS70/SOC report done by a 3rd party auditor, etc.

There are so many different nice's that are federally regulated that it would be best to concentrate on a few and slowly expand as you learn more about other requirements (and make the changes necessary in your code).