They're all good apart from "Do you want me to gain weigh". It should say "Do you want me to gain weight" with a t at the end of weigh. Do you want me to get fat is the most common, in my opinion.

They're all fine. I'm sure you already noticed the little spelling and punctuation missing at the end of the third sentence. However, they're not all polite. Whether you should actually say them would depend a great deal on the person you're directing them at. Would it be culturally very rude to refuse the food? Is that person in a position of authority or demanding of respect? A stranger? A friend? A family member? You would want to think about all of those sorts of things.