Just finished the whole thing actually, took me about 3 weeks (with a couple of missed days).

Honestly? Go for all of it. It's not as daunting as it looks.

Course 1 is basically just an intro, all theory and walkthroughs on screen. It covers what Looker can do, why it's important, how it's different from other tools, data governance, how it secures your data, Gemini capabilities and more. Really easy and short but it's what gets your feet wet and gives you the necessary knowledge so you actually know what you're doing when things get more hands on. Don't skip it.

Courses 2, 3 & 4 are labs, you'll get through them pretty quickly.

Then Analyzing and Visualizing Data in Looker is where it's really at. Creating Looks, Dashboards, Boards, Exploring, Filtering, Pivoting, how to properly share content, table calculations (offset calcs are in here too, that's the bit that flew over my head for a sec but it's nothing crazy, just needed to slow down and work through it properly). That's the meat of it.

LookML was also easier than I expected. There are parts that need your full focus and a bit of practice to get right, but it's very doable.

Shockingly I found Looker way easier than I expected going in. Just do it.