A local institution is looking into having a web app designed, through a course of events, I semi-volunteered. This is a large project for me, any tips on how to approach?

Here is an outline of the project:

I am not a web-dev super star (I code games/apps in java for phone as a long-time hobby) - was curious just how I should most efficiently approach this site design.
I feel it is as simple as: Make a website that has login options for the 3 different types of members.
Each member sees a different home page when they log in.
Data is stored directly into a MySQL database using php (it seems there is a lot of support for php if I have questions, is another language better for this?).
Permissions for viewing information, permissions for allowing certain things to happen in the database (i.e. a student not being able to apply for two classes that occur simultaneously) - Not sure if I could do all of this directly in the html form, or if I would need to get java involved somehow.
I do not think anything is beyond my coding capabilities (+google), but wanted to make sure I was approaching the situation with the best available tools / languages.
Any tips would be appreciated.