This was beautiful. I knew something was up early on - I saw numbers begging to be marked in puzzle 5 - but it wasn't until puzzle 8's little drawings (and of course puzzle 7 making it clear we're solving Angle Searches now) that the true nature of the puzzles was clear to me. I promptly went back to solve all of them properly before moving on; I did of course get the remaining-letter messages right away (in part because I subscribed to Games magazine in the 80s and always check for those, and in part because of the 'foe carton' XD). I promptly saw the mirroring of the right-side clues; I didn't realize the significance of the letter/number pairs at the bottom of each page until puzzle 11 (the 'foe carton' was an especially nice way of confirming that), and it was only after catching that did I realize all puzzles had exactly twelve entries (despite solving ten of them already) and that their ordering around the blue line matched the bottom (except where duplicates were involved - the way that was subtly clued with the two Zodiacs was sublime)... which is exactly what I needed to find 'leftovers' in there to finish it! I saw puzzle 0 was labelled "Rules" and utterly refused to look at it any further than that (checking it afterward confirmed it told me nothing I didn't already know, although the full 150 mentioned on the back page clearly counts the six terms there) - if I were to present this to my friends, I'd omit that page entirely, as it breaks the flow of the rest of the puzzle set and feels like a slap in the face ("All that clever stuff you figured out? Wasted effort, I was gonna tell you all along."). But maybe that's just me being a professional puzzlesmith. Anyway, puzzle 12's assembly handily redeemed any bad blood from the previous page, laying bare just how genius all this comes together, and the self-reflexive final answer reveal is one of the most satisfying things I've encountered in any puzzle ever.
Also, yay, dwarf planets! And I wonder how many people knew of 'lengua de gato' right off the bat (I certainly didn't) and caught a theme immediately. (Cookies being "little warm-ups" is a TOP-TIER fridge-logic hint and I'm guessing most solvers never realized it at all!)
The only criticism I could levy is that some of the puzzles technically had multiple solutions with how the letters in the grid are apportioned to the words (such as the 'ra' at the start of 'rat' and 'rabbit' in puzzle 2), but none of the remaining-letter messages are affected by that (and of course puzzle 6 is that way unavoidably and hilariously) except of course for needing to choose the right 'a' in puzzle 11 (which is obvious enough). I also really wish there was no puzzle 0, but I understand why it's there - I can't fault that.
For the record, I solved this entirely on paper, with the "for printing" edition of the file. I used a highlighter to start, inspired by how 'eclipse' is pre-marked in puzzle 1... which proved to be an unforseen boon, as it didn't interfere with when I used a pencil once I started actually solving the puzzles XD