1. General impressions of the book:

It's much more readable than the last book, after all, it's a novel. My first impression is, I will get that 100 yuan back! Thanks to the always "f**ked" Martian I am not f**ked this time.

The everyday math Mark does for his survival on how to get enough food, calories, water, oxygen, hydrogen and so on, reminds me of my everyday math on how to pay my credit card.

It's humorous, easy to understand, though with a lot of math to do (can't help myself from calculating), and I didn't quite get some details in Chapter 5 when Mark messing up with the gases, how does he get enough containers, but as a science fiction it's written in a reader-friendly way as a whole. 

2. 

3. I suppose Sol means a solar day on Mars.