Is there an environment where I can test some of the admin features like customizing the dashboard? I have no idea what is configurable and what is fixed 
Yes, Linchpin Intranet is very transparent and easy to test. We have a Getting Started with Linchpin section on our website that will explain how to proceed.
Admin account
Customer Administrator: A customer administrator login with extended rights that let you access configuration pages of the most important Linchpin settings and plugins.
username: pwinter, password: pwinter (English)
username: tschroeder, password: tschroeder (German)
Create your own test instance
Instead of testing the public Linchpin demo instance you can create your own instance with a click. It’s up and running within an hour and free. We even help customizing the design if you ping us.
Get your own instance up and running now. It has the same logins at first. For security reasons you may want to change that.