I think you did a great job showing the process of UbD as well as how nicely NGSS fits into the UbD model. UbD is all about those big ideas, and it seems NGSS is as well.
When I think about UbD, I like to think about the 40-40-40 rule. A few different UbD resources mention this and the frame is nice. The idea is that there are things that are important to know and do for about 40 days, other things for about 40 months, and finally some things that are important to know, do, and understand for 40 YEARS. I think in school we spend a lot of time with the 40 day stuff and some time with the 40 month stuff...not enough time with the 40 year stuff.
Some UbD templates help categorize these ideas in different ways. One of my favorite is via assessment. Assessments that use multiple choice, fill-in-the-blank, and other declarative type responses are probably after the 40 day and 40 month stuff. Performance assessments, that are real world, complicated, messy, creative, many right answers, etc...those are the 40 year type assessments. Another way I like to look at it is through the Google lens. If you can Google it and understand it within a click or two or minute or two, it is probably a 40 day level learning. This is not to say that these things are not important, but in all reality, this type of knowledge can literally live in someone's pocket. Using that knowledge, thinking critically and creatively, asking questions, communicating ideas, analyzing data...you can't Google that. NGSS and UbD seem to have their sights set on those things.
With that said, I would put all three dimensions (practices, CCCs, DCIs) into the "big idea/enduring understanding) category. The box lower down that says "do" I think are more discrete skills that are needed in order to do something else. I think of these as skills that are needed to, say, analyze data. The essential questions, in my general practice, take the big ideas/enduring understandings, and create questions out of them that lead to the assessments. Again, the awesome thing about NGSS is that the assessment piece is already started for us through the performance expectations. I am really excited to start digging into this more.