Adding features to a Invoicing Software

Hello, I am looking for someone to help me create a powerful invoicing software which can help my business operations run more smoothly. I need to add some features to this existing software including ones that are analytical, have enhanced security and payment systems. The complexity of these features will be low, so they should not require a huge amount of time to develop. I do not have a specific list of features in mind, and I am open to any suggestions the freelancer might have.