Build a Website

Hello Freelancers, Please note that if i refer to 'software', i mean the system i am looking to create. I'm open to the technology (Lanuages & DBs) used, however the interface must be 'skinnable' (hence bootstrap or any alternative), easily updateable and fairly future proof, but most of all - SECURE. The software must function in a way where we can create or offer an API at a later date to allow other programs to use functionality within the website. What i'm looking to do is create a SECURE online Financial data entry portal for a number of currently existing XML Files. These are templates and the structure cannot be changed by the user, however can be altered over time to include more/less/changed. The software can translate the XML into whichever format you're comfirtable with, but the input to the system (to update the files) will be XML, and the end case output has to be XML. There are around 60+ XML Files that need to be scanned and version controlled by the system to ensure the user is using the most current version; however the user and system must be able to have the option to select which version of the templates are used. This is going to be the first version of the software and i will not require it to look great, but have the types of functionality i've listed. Multiple future versions will likely be added in short successions of functionality,