The majority of questions on a given LSAT are around 2-4 star difficulty. If I had to put rough numbers on each, I'd probably say there's around 10 one stars, 25 two stars, 35 three stars, 25 four stars, and 10 five stars. Obviously give or take on those figures since they're just rough estimates but yeah most of the material you see on test day is "moderately" difficult.

In my admittedly limited personal experience, this is a very normal part of the process and isn't indicative that you've "topped out." It obviously depends on what score range you're plateauing in, I'm inferring that you're around the low-mid 160s, but it mostly indicates that you have a good grasp of foundational skills but haven't yet arrived at the level of speed or accuracy to break through into higher ranges. Changing study habits or simply taking some time off could be beneficial in getting there, but no need to worry about being stuck here forever lol

I took a PT near the end of the core curriculum because, like you, I was craving another benchmark to view my progress. I would say you're probably at the point where you can comfortably take another, but I'd wait until after you're done with the core to take more so you can get the absolute most out of them.

I typically use the written explanations for help with understanding why the wrong answers are wrong but the video explanations to help with understanding why the right answers are right. I personally find that JY sometimes brushes off answer choices that I might have picked without giving much of a formal explanation as to why they're wrong so reviewing a more dedicated explanation available for every answer choice on every question more frequently triggers me to understand what I did wrong. But JY also gives more detailed and logically intuitive explanations as compared to the written explanations for why the right answers are right which more frequently triggers me to understand what I did right. I also find JY's breakdown of the stimuli to make more sense on average than the written explanations.