programming languages for online accounting software [on hold]

Hi I want to create my own online accounting software which can

1. Support databases and
2. different people with different access rights can access it
3. and process data and it can create complex reports based on search queries.
4. Also I want it to be accessible without installing additional softwares.
5. It must be secure so not easily hackable.

I know basic html and advanced Excel Macros. Now which programming languages/things/techniques I need to learn? I want to be focused right from start and need to set my goals from here so I may not end up in another destination when I have learned something.