Web applications - combine or separate?

For our company I'm creating a big Extranet website which will feature a set of sub-applications. I'm a bit puzzled by what should be the right setup of the solution and projects.

I have one web application that we call the Portal. It contains the authentication/authorization classes, masterpages, navigation/url routing classes and theme definitions. It will also contain some basic overviews for our customers to get a quick idea of their project status.

In the coming year we are going to develop and integrate more applications with the portal. Think of it as detailed overviews and tools called Feature A, B and C. Over the years we will improve these applications and release new versions. These web applications should fit into the navigation of the Portal seamlessly. I'd like them to reuse the masterpages and themes.

What is the proper way to setup this solution?
How can I tie the applications together, re-use the master pages and keep it maintainable?
How can I share certain webcontrols (ASCX) in a proper way?
We are using TFS, perhaps any branching/merging ideas?

Edit:
I'd like to create it in ASP.Net WebForms, we have the most experience in that area. But basically we can use anything, we've got the webserver under our own control (as long as it is Microsoft oriented, not switching to php or something like that :))

What is the proper way to setup this solution?

The proper way... There are so many. I have seen a lot of applications, and a lot of different setups (a lot of which that I would deem "proper"). What you're really asking is for the best way for your situation.

Because you're building a portal, you'll have the luxury of feature separation which will help you as you develop additional features for your application.

I would setup a single website with a separate folder for each feature. Making it a single website will allow all features to share the same masterpages, usercontrols, and configuration file - without having to do anything special. (On that note, I would put all your master pages in a folder by themselves, and create another folder for your usercontrols).

How can I tie the applications together, re-use the master pages and keep it maintainable?

Again... folders are the best option here. Folders will help separate each feature, making the application easy to manage.

How can I share certain webcontrols (ASCX) in a proper way?

First of all, ascx files are not webcontrols. They are usercontrols. WebControl is a class for creating server controls that reside in a separate assembly. Regarding usercontrols, as I said above, if you put them in a separate folder, they're always in one place and available throughout the application.

We are using TFS, perhaps any branching/merging ideas?

There really isn't anything special you need to do here. There are a lot of different paths you can take regarding branching:

• One is to create a branch for every release.
• Another is to create a branch for every new feature you add (in your case, this is pretty much the same as the first option).
• Yet another is to create a branch for each developer.

When I decide how I am going to branch my code, I think about what will protect me the most. In your case, you need to plan for bug fixes in between feature releases so maybe one branch after each release makes the most sense (call it your dev branch). Given the separation of features, though, one feature may not effect the rest of the application. You may not need this kind of branching to be safe.