MS Access + SQL Server for 1160 users - Is it worth it? (Please Help!)
This sounds like an enormous project.

My advice is to go back and look again for an open source, off-the-shelf product that meets your main needs.

It is difficult to believe that your school is alone in its needs and that no-one else has similar requirements.

Even if you the system does not do everything you require, as long as it is built in an open way, with a sound underlying data model then you will be able to extend it with small additional components.

I would also be careful to manage expectations and let people know that the system will not meet all their needs to start with.

good luck!