Online services website with some custom features

We are a online bookkeeping company which provides services to the small businesses. We are looking to add features bookkeeping website. This project is for professional with past experience in similar area. Security is our main concern, we want to make the website secure as possible. Please try “read it got it” in the proposal text to be considered for this project. Here are some of the required features. We have three or four services plans which we offer to the customers. We provide one month free trial period, customer should be able to sign up by providing person/company information. member should provide payment information such as Credit card or Echeck. Transaction should only be posted after 30 days based on the plan selected by the customer before signup. If the customer decides to cancel the service before 30 days, we should have to option to cancel the transaction. Registered member frontend area: member should be able to edit profile, update payment information, change service plan, upload multiple format files search files based on period export files Admin backend We are looking for a simple and secure backend app to manage clients data, we want it to be open source. Please provide your recommendation, it should be open source and have all the basic features such as: customer management payment management reports email customers customer service tools email notifications Any other features that can be useful please let us know, we are always open to the idea. Custom features: Our customers upload files to ftp directories, we need these individual directories to be assigned to individual customer. User/staff accounts with permission, assign individual customer file directories to user. Security Security is our main concern, please tell us what is your plan to make our site more secure. The site should be secure from front and backend. SSL needs to be installed, All security holes need to be closed, xss attacks preventing, all forms need to be secure by properly filtering the data, any and all other security measures need to be taken to prevent any security threat. Please bid accordingly and have your references ready.