hey could someone make a guide for how to get as big as possible
You can eventually unlock a semi-secret shop in the top right part of the farm that sells liquid nutrition, which gives you +25 nutrition without counting as a meal for the day, so just save up money, buy as many of those as you can, and profit in the belly department.
EDIT: Did some testing and you need a total of 600 nutrition to hit max size. Good luck!