very simple whmcs module

Hi There, I need a very simple whmcs module to be developed. 1. Allow client to upload bank in slip in jpg, png or pdf format as attachment to each invoice, once done payment 2. admin can refer back the each invoice bank in slip attachment(note different invoice different bank in slip). 3. click attachment to show the jpg in another tab/window and/or point the attachment will pop up the attachment. There will be no upfront milestone. Minimum bid will be qualified. It will be an start for long term relation. Thanks