Hi!!! I've spent the past few hours figuring out how to decompile the game, and I can confirm some of what you're saying! I had just been trying to grab the different transformation forms, but I ended up recovering the original code too. I'm trying to sift through it right now, and am working on a Google Sheets file with information.
1) Based on what I've figured out, the game creates a pool of potential items based on what you drop in. Items are added to the pool after a certain amount of yen is added, so that means that if you're below a certain number, those higher items are impossible. Everything less than 100 is guaranteed to be apple seeds.
2) Can confirm! The hungry line is actually titled as the anorexia line in the files. There's also the default sprites, anomolous line, holllow bride, parasite line, perfect line, and the unhealthy line.
3) Unsure
4) Going based off of what I said in #1! After 100 yen, some more items start being added to the pool. For example, at 100 there's molded bread, sun dried termites, cicadas, soft drinks, water bottles, etc. The higher you go, the more items are added to the pool, including better ones. Items are added at 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 50, 100, 150, 200, 300, 400, 500, 600, 700, and 1,000 yen. I don't think that other misc increments between the item limits affect what you get, so it's better to save up.
5) This is true for some of the lines! The healthy and unhealthy lines have 5 transformations, but the others have only 3.
6) In the code, items are tagged with being either "healthy", "unhealthy", "liquid", "parasite", and "anomaly". Some of the items can have 2 of the tags at a time. Interestingly, the food sprites are bundled into "anomalous", "disturbing", "normal", and "specials". I think only the tags influence things though!
7) Unsure
8) I think that that's a good way to summarize it! Hoard the food you need for your transformation line.
