Wordpress: Need secure backend with upload/download & archive

I need a secure backend for a small accountant/bookeeper website that is being built with wordpress. The site will have the following features: 1) Clients will be able login to secured area and upload documents to Admin (Either admin or system will generate login credentials for client, which will be sent to client from within the system) 2) Admin will be able to upload documents to client's page. Only that client will be able to see the files that are specifically for him. 3) All files exchanged between client and admin needs to be archived, and client will have access to the archived data. The security features need to be integrated with the mysql db, to better control access permission, and all data securely stored in the db. In addition to the functionality, the backend should have an attractive look and feel, and easy for the end user to use. I really need someone with strong db security skills, along with the other skills needed to complete this task. This job has to be completed within 5 days. There may be plugins and scripts available that have most of these features already, which will lessen the time on this project, but it must be secure and work as described. This is not a difficult task for someone who know what he/she is doing. Will pay a bonus if the job is delivered on time and fully working.