Kind of two different questions here but I figured I'd ask.
1. How many endings are you planning for the base game out of curiosity?
2. Do you plan on making more unique interactions with people when Mari is at her maximum weight?
3 major different endings, with a few variations each. I believe it would make 7-8 total.
For your second question, yes I try to add them here and there as I write. As the game grows there's many characters and dialogue, but I try to keep up.