We used to have only one web app, but now we are breaking it down into multiple ones. Each one will be packaged as separate product (web app) Some have things in common some do not.

It was originally coded with php and using Postgresql 8.4 and CodeIgniter as the framework.

I am looking for some good suggestions on how I should set up multiple web apps. They all have their own somewhat unique data. Some data in the databases can be common to some apps but not all. All the apps will be on one server and will have some kind of API to manipulate data.

I want it to be structured such that one User account can access any product they purchase. (kinda like google accounts)

I do not know if its a good idea to have multiple database, or just to have one big one. eventually we will be using S3 for some videos and other images.

Your thoughts and suggestions are much appreciated.