Thank you for this subject, very informative ! Let me share my (modest) work about self-sufficient farming, with crop combinations and placement. It's quite simple as it is intended to teach my DST friends about the new farming update. It may won't add much to what all of you did, but maybe you'll find few ideas
Veggies combos (seasons, nutrients)
Here is the summary I did about 2-veggies and 3-veggies combos. Since most of the vegetables are available with 1-1 and 1-1-1 ratios (and since I wanted to keep it simple for my friends, especially with placements afters) I didn't considered the more complex ratios like some of you did.
Seeds disposition on the tile
For my part I focused on the minimum space needed to grow my 2 or 3 vegetables combos --> as 1x1 is too small for 3-veggies combos, it's 2x1 tiles then. The 2x2 configurations give me so much food that it's often a waste...
I work too with the "Snapping tills" mod (https://steamcommunity.com/sharedfiles/filedetails/?id=2302837868).
In my 2x1 field, it allows me to draw a 4x7 grid (kinda strange, the middle raw among 7 looks just in the middle of the two tiles. Since I don't know to which tile the crop and nutrients count in this middle raw, I prefer to keep it empty). Thus, I use a 4x3 + 4x3 grid, one on each tile.
Here is two the best dispositions I have :
1/ Perfect nutrient neutrality, but 2 of the 18 crops are not giant
2/ Perfect giant crops (20/20), but as there are 1 more type-3 crops on each tile, it requires a little bit of the corresponding fertilizer.
A simple example of the Garlic/Onion/Pepper combo, with my disposition 2 (requires 4x8=32 compost units = 1,33 compost item for each tile).