If you're going to use the IIS web server on SQL Server, the best choices are going to be one of the .NET languages from Microsoft.
However, the best choice is simply to use what you are familiar with.
If you need to learn something from scratch for this, I'd go for C# with a Microsoft backend, or use PHP and MySQL if you want to go down the open source route.
Before you do go ahead though, I'd check the cost of consultants or contractors in your area with expertise in this system in case things come up that are beyond you.
John