Well...the first and obvious step would be to get the solution running in debug mode.  You'll want to have this setup so that you can run the DotNetNuke.sln or your own solution if you chose to reference by file rather than project.

The tough part will be the password since this is stored in encrypted format.  You need to know where/when/and how you want to decrypt this and be careful not to pass a user's pwd around unecrypted in a URL string.  This could be an interesting challenge.  Have you decided which application will sync the pwd's or will there be a "master" program or service to do this for you?  OWA may be tricky here because you will be using an exchange server which will have its own security/authentication methods.  I would certainly draw this up prior to wrting a line of code so you know how this information will or can be communicated with each system.

Good luck!

John