Modifying Tails OS

Hi, I am a CS major, and I am taking a course in Operating Systems. My professor has assigned a project where I need to modify Tails OS and add these features:

• Custom encryption algorithm for storage.
• Replace the default browser with a hardened version of Firefox.
• Implement user-controlled firewall rules.

I am not able to connect any of these with my coursework. Can anyone please help me get started?