Yes, most of a shock caloric increase leaves as poop and NEAT. There’s no hard limit because it varies widely between people. Biology is messy.

Only so much of those 35,000 calories will be converted to fat. The bulk of it will pass though before that happens. Most people wouldn't even be able to consume that many calories without the body reacting negatively.

All mammals become overweight by consistently eating more calories then they burn. The occasional pigout is pretty much lost in the average if it's a rare event and the person maintains a healthy diet otherwise. Once a month, no worries. Once every other day, you'll need new pants.