You seem to have the flexibility to take the time for long periods of focus work. You are not afraid of a good challenge!

To create your Service Design Principles Library I suggest you check your calendar and block two times 2 days of sprint. In the first sprint you might come up with a list of principles and for each principle write just a title. And in the second sprint you might do the writing for each of these principles.

Your strength and resources

1. You have flexibity with your calendar

2. You can focus during long hours on the same challenge

What you might lack

1. You are not process driven

2. You don't have a budget for tools or external help

How to go further

Read the book Deep Work to make the most of your your focus time.