Thank you for taking your time to read and answer.
C might be used in the project. It could be used for driving a high traffic shop's front end or could be used for an API. This is not something I really want to do, but it's a possibility. I figured it will raise some discussion :)
I would prefer to support both Apache and IIS.
Database-abstraction layer is a great idea. And multiple database support was something I thought about, but did not include into the outline. I think all development will be done on MySQL anyways.
JavaScript use will be very limited. JS will be used to enhance user experience. No critical features will be written in JS.