If you are planning to sell software to the government or business as a startup, consider
source code escrow. Your customers will tend to stick with established vendors for fear of you going out of businesses and leaving them with an unsupported implementation. The source code escrow is insurance against that being more of a catastrophe for your customers than you.
Invest in dedicated technical support. It plays up as great comedy in the movie, Office Space, when the character says you don't want the customers talking directly to the engineers.
You actually don't want that. Establishing a quality support team keeps the engineers productive on developing while the support group ensures the customers are getting help with their issues. Oh, and don't outsource this responsibility to a foreign country. If you think you can't afford quality support, at least staff it with a recent college grad and split that person's time between support and bug fixing.