many of the project types have a page in the project customizer that allow you to add a dependency on a Project.

Pressing the Add Project button seems like it always opens up a fancy file chooser dialog in some default location...
which is almost always wrong [at least the first time].

It would be nice to be able to press a button to select one of the projects that is already open in the IDE....

Consider the following steps...

Create a new web app project.
Create a new java library project.

Then try to make the web app depend on the java library.  It is possible. but it can be pretty painful, if the two
projects are in different sub directories....

BONUS POINTS: implement a DnD to create the dependencies... (select java library project... drag onto web app project...
drop... defines a dependency...)