I think it depends how you usually study. If you can read and retain, I see no reason to take notes unless something is harder for you to grasp.
Personally, I’ve been taking far more notes than I usually do. It slows my reading down a bit which I think is important.
I’d take the cold diagnostic when you have a chance. Personally, I think it’d be fine to read a brief intro on LG, so you have some remote clue what is going on. I scored fairly high [but I didn’t really take it as a diagnostic… i.e. didn’t just sit down and knock it out]. I wouldn’t worry…especially if you lose most of your points in LG and LR. Those sections have the most room for improvement. RC is a bit trickier, but there is definitely room for improvement depending on what is tripping you up.